/* ===== Reset & Design Tokens ===== */
:root {
  /* Core colors — warm educational palette */
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --primary-light: #dbeafe;
  --primary-subtle: #eff6ff;
  --success: #16a34a;
  --success-light: #dcfce7;
  --danger: #dc2626;
  --danger-light: #fef2f2;
  --warning: #d97706;
  --warning-light: #fef3c7;

  /* Neutral palette — warm stone tones */
  --bg: #f4f5f7;
  --bg-alt: #eef0f2;
  --card-bg: #ffffff;
  --text: #1e293b;
  --text-secondary: #475569;
  --text-light: #94a3b8;
  --text-muted: #cbd5e1;
  --border: #e2e8f0;
  --border-light: #f1f5f9;

  /* Shadows — layered for depth */
  --shadow-sm: 0 1px 2px rgba(0,0,0,0.04);
  --shadow: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
  --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.07), 0 2px 4px -1px rgba(0,0,0,0.04);
  --shadow-lg: 0 10px 25px -5px rgba(0,0,0,0.08), 0 4px 10px -5px rgba(0,0,0,0.04);

  /* Radii */
  --radius: 8px;
  --radius-sm: 6px;
  --radius-lg: 12px;
  --radius-xl: 16px;

  /* Typography scale */
  --text-xs: 0.75rem;
  --text-sm: 0.8125rem;
  --text-base: 0.9375rem;
  --text-lg: 1.0625rem;
  --text-xl: 1.25rem;
  --text-2xl: 1.5rem;
  --text-3xl: 1.875rem;

  /* Font stacks */
  --font-ui: 'PingFang SC', 'Microsoft YaHei', 'Noto Sans SC', -apple-system, BlinkMacSystemFont, 'Segoe UI', 'Helvetica Neue', sans-serif;
  --font-content: 'Noto Serif SC', 'Source Han Serif SC', 'Songti SC', 'STSong', 'Georgia', 'Times New Roman', serif;
  --font-mono: 'JetBrains Mono', 'Cascadia Code', 'Fira Code', 'SF Mono', 'Consolas', 'Menlo', monospace;
  --font-display: 'PingFang SC', 'Microsoft YaHei', -apple-system, BlinkMacSystemFont, sans-serif;
}

* { margin: 0; padding: 0; box-sizing: border-box; }

html { font-size: 16px; -webkit-text-size-adjust: 100%; }

body {
  font-family: var(--font-ui);
  font-size: var(--text-base);
  line-height: 1.6;
  background: var(--bg);
  color: var(--text);
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}

::selection { background: var(--primary-light); color: var(--primary-dark); }

/* Scrollbar refinements */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--text-muted); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: var(--text-light); }

/* ===== Header ===== */
.app-header {
  background: linear-gradient(135deg, #1e40af 0%, #2563eb 100%);
  color: #fff;
  padding: 0 16px;
  height: 56px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  box-shadow: 0 2px 8px rgba(30,64,175,0.2);
  position: sticky;
  top: 0;
  z-index: 100;
  gap: 12px;
}
.app-header h1 { font-size: var(--text-lg); white-space: nowrap; font-weight: 700; letter-spacing: 0.01em; }
.header-brand { display: flex; align-items: baseline; gap: 10px; flex-shrink: 0; }
.header-brand h1 { font-size: var(--text-lg); }
.header-tagline { font-size: var(--text-xs); opacity: 0.7; display: none; letter-spacing: 0.02em; }
@media (min-width: 640px) { .header-tagline { display: inline; } }
.user-profile-btn {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 4px 12px 4px 4px;
  border: none;
  border-radius: 100px;
  background: rgba(255,255,255,0.12);
  color: #fff;
  font-size: var(--text-sm);
  cursor: pointer;
  transition: all 0.2s;
  backdrop-filter: blur(4px);
}
.user-profile-btn:hover { background: rgba(255,255,255,0.22); transform: translateY(-1px); }
.user-avatar {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 30px;
  height: 30px;
  border-radius: 50%;
  background: rgba(255,255,255,0.25);
  font-weight: 700;
  font-size: var(--text-sm);
  color: #fff;
  flex-shrink: 0;
  border: 1.5px solid rgba(255,255,255,0.15);
}
.user-name {
  max-width: 80px;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.header-icon-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 34px;
  height: 34px;
  border: none;
  border-radius: 50%;
  background: transparent;
  color: #fff;
  cursor: pointer;
  transition: all 0.2s;
}
.header-icon-btn:hover { background: rgba(255,255,255,0.18); transform: translateY(-1px); }
.main-tabs {
  display: flex; gap: 4px; margin: 0 auto;
}
.main-tab-link {
  color: rgba(255,255,255,0.75);
  text-decoration: none;
  padding: 6px 16px;
  border-radius: 100px;
  font-size: var(--text-sm);
  font-weight: 500;
  transition: all 0.2s;
  letter-spacing: 0.01em;
  position: relative;
}
.main-tab-link:hover { color: #fff; background: rgba(255,255,255,0.15); }
.main-tab-link.active { color: #fff; background: rgba(255,255,255,0.2); }
.main-tab-link.active::after {
  content: '';
  position: absolute;
  bottom: -2px;
  left: 50%;
  transform: translateX(-50%);
  width: 20px;
  height: 3px;
  background: #fff;
  border-radius: 2px;
  opacity: 0.7;
}
.tab-icon { display: none; }
.header-actions { display: flex; gap: 8px; align-items: center; flex-shrink: 0; }
.header-actions button {
  background: rgba(255,255,255,0.15);
  color: #fff;
  border: none;
  padding: 6px 12px;
  border-radius: 100px;
  cursor: pointer;
  font-size: var(--text-xs);
  white-space: nowrap;
  transition: all 0.2s;
  backdrop-filter: blur(4px);
}
.header-actions button:hover { background: rgba(255,255,255,0.28); transform: translateY(-1px); }

/* ===== Layout ===== */
.container {
  max-width: 1040px;
  margin: 0 auto;
  padding: 20px 24px;
  transition: max-width 0.3s ease;
}

/* Wide layout toggle — utilize screen space */
body.layout-wide .container {
  max-width: 100% !important;
  padding-left: 40px;
  padding-right: 40px;
}
body.layout-wide .kp-article {
  max-width: 100% !important;
}
body.layout-wide #main-content {
  background: #fff;
}
/* Flash header bar to indicate toggle worked */
body.layout-wide .app-header {
  background: linear-gradient(135deg, #1e40af 0%, #2563eb 100%);
  box-shadow: inset 0 -2px 0 rgba(255,255,255,0.1);
}

/* Layout toggle button in header */
.layout-toggle-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 4px;
  min-width: auto;
  width: auto;
  height: 32px;
  border: 1px solid rgba(255,255,255,0.35) !important;
  border-radius: 100px !important;
  background: rgba(255,255,255,0.12) !important;
  color: #fff;
  cursor: pointer;
  padding: 0 14px !important;
  font-size: var(--text-xs);
  white-space: nowrap;
  transition: all 0.2s;
  backdrop-filter: blur(4px);
}
.layout-toggle-btn:hover { background: rgba(255,255,255,0.25) !important; transform: translateY(-1px); }

/* ===== Cards ===== */
.card {
  background: var(--card-bg);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 20px;
  margin-bottom: 16px;
  transition: box-shadow 0.2s;
}

/* ===== Platform Intro ===== */
.platform-intro {
  display: flex;
  align-items: flex-start;
  gap: 18px;
  background: linear-gradient(135deg, #f0fdf4 0%, #fefce8 50%, #eff6ff 100%);
  border-left: 4px solid #059669;
  padding: 24px 22px;
  margin-bottom: 24px;
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
}
.platform-intro .intro-icon {
  font-size: 2.5rem;
  line-height: 1;
  flex-shrink: 0;
  margin-top: 4px;
}
.platform-intro .intro-text h2 {
  font-size: var(--text-xl);
  margin-bottom: 6px;
  color: #065f46;
  font-weight: 700;
  letter-spacing: 0.02em;
}
.platform-intro .intro-tagline {
  font-size: var(--text-base);
  font-weight: 500;
  color: #059669;
  margin-bottom: 8px;
}
.platform-intro .intro-desc {
  font-size: var(--text-sm);
  color: #4b5563;
  line-height: 1.7;
  margin: 0;
  max-width: 640px;
}

/* ===== Top-level Category Tabs ===== */
.top-cat-tabs {
  display: flex;
  gap: 4px;
  margin: 16px 0 20px;
  border-bottom: 2px solid var(--border);
  overflow-x: auto;
  -webkit-overflow-scrolling: touch;
}
.top-cat-tab {
  padding: 12px 24px;
  border: none;
  background: transparent;
  font-size: var(--text-sm);
  font-weight: 600;
  cursor: pointer;
  border-bottom: 3px solid transparent;
  margin-bottom: -2px;
  transition: all 0.15s;
  white-space: nowrap;
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text-secondary);
  font-family: var(--font-ui);
}
.top-cat-tab:hover { background: var(--primary-subtle); color: var(--primary); }
.top-cat-tab.active {
  border-bottom-color: var(--primary);
  color: var(--primary);
}
.top-cat-tab .tab-icon { font-size: 1.1rem; }
.top-cat-tab .tab-name { font-size: var(--text-sm); font-weight: 600; }

.sub-cat-panel { margin-top: 8px; }

/* ===== Exam Type Grid ===== */
.exam-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(150px, 1fr));
  gap: 14px;
  margin: 16px 0;
}
.exam-card {
  background: var(--card-bg);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow-sm);
  padding: 20px 14px;
  text-align: center;
  cursor: pointer;
  transition: all 0.2s cubic-bezier(0.4, 0, 0.2, 1);
  border: 1.5px solid var(--border);
  position: relative;
  overflow: hidden;
}
.exam-card::before {
  content: '';
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  height: 3px;
  background: var(--primary);
  opacity: 0;
  transition: opacity 0.2s;
}
.exam-card:hover, .exam-card:active {
  transform: translateY(-4px);
  box-shadow: var(--shadow-md);
  border-color: var(--primary);
}
.exam-card:hover::before { opacity: 1; }
.exam-card.active { border-color: var(--primary); background: var(--primary-subtle); }
.exam-card .icon { font-size: 2rem; margin-bottom: 8px; display: block; }
.exam-card .name { font-size: var(--text-sm); font-weight: 600; color: var(--text); }
.exam-card .count { font-size: var(--text-xs); color: var(--text-light); margin-top: 4px; }

/* ===== Filter bars ===== */
.filter-bar {
  display: flex;
  gap: 10px;
  flex-wrap: wrap;
  margin: 16px 0;
}
.filter-bar select, .filter-bar input, .filter-bar button {
  padding: 9px 14px;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  background: var(--card-bg);
  font-family: var(--font-ui);
  color: var(--text);
  transition: border-color 0.15s, box-shadow 0.15s;
}
.filter-bar select:focus, .filter-bar input:focus { border-color: var(--primary); box-shadow: 0 0 0 3px rgba(37,99,235,0.1); outline: none; }
.filter-bar button {
  background: var(--primary);
  color: #fff;
  border-color: var(--primary);
  cursor: pointer;
  font-weight: 500;
}
.filter-bar button:hover { background: var(--primary-dark); }

/* ===== Problem Set List ===== */
.pset-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
  cursor: pointer;
  transition: all 0.15s;
  border-radius: var(--radius-sm);
  margin: 2px 0;
}
.pset-item:hover { background: var(--primary-subtle); }
.pset-item .title { font-size: var(--text-base); font-weight: 500; color: var(--text); }
.pset-item .meta { font-size: var(--text-xs); color: var(--text-light); margin-top: 2px; }
.pset-item .arrow { color: var(--text-muted); font-size: 1.2rem; transition: transform 0.15s; }
.pset-item:hover .arrow { transform: translateX(3px); color: var(--primary); }

/* ===== Mode Selection ===== */
.mode-select {
  display: flex;
  gap: 16px;
  margin: 20px 0;
}
.mode-card {
  flex: 1;
  background: var(--card-bg);
  border: 2px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 28px 20px;
  text-align: center;
  cursor: pointer;
  transition: all 0.25s cubic-bezier(0.4, 0, 0.2, 1);
  position: relative;
  overflow: hidden;
}
.mode-card::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  right: 0;
  height: 4px;
  background: var(--primary);
  transform: scaleX(0);
  transition: transform 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}
.mode-card:hover, .mode-card.selected {
  border-color: var(--primary);
  box-shadow: 0 4px 16px rgba(37,99,235,0.1);
  transform: translateY(-2px);
}
.mode-card:hover::after, .mode-card.selected::after { transform: scaleX(1); }
.mode-card .mode-icon { font-size: 2.2rem; margin-bottom: 10px; display: block; }
.mode-card .mode-title { font-weight: 700; margin-bottom: 6px; font-size: var(--text-base); }
.mode-card .mode-desc { font-size: var(--text-xs); color: var(--text-light); line-height: 1.5; }

/* ===== Practice Page ===== */
.practice-header {
  display: flex;
  align-items: center;
  gap: 14px;
  padding: 14px 0;
  border-bottom: 1px solid var(--border);
  margin-bottom: 16px;
  position: sticky;
  top: 56px;
  z-index: 10;
  background: var(--bg);
}
.practice-header .practice-title {
  font-size: var(--text-lg);
  font-weight: 700;
  margin: 0;
  flex: 1;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
  color: var(--text);
}
.practice-header .btn-back {
  flex-shrink: 0;
}
.practice-layout {
  display: grid;
  grid-template-columns: 1fr;
  gap: 16px;
  max-width: 100%;
}
@media (min-width: 768px) {
  .practice-layout { grid-template-columns: 230px minmax(0, 1fr); }
}

.question-nav {
  background: var(--card-bg);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow);
  padding: 16px;
  position: sticky;
  top: 122px;
  max-height: calc(100vh - 140px);
  overflow-y: auto;
  align-self: start;
}
.question-nav h3 {
  font-size: var(--text-sm);
  margin-bottom: 10px;
  color: var(--text-light);
  font-weight: 600;
  letter-spacing: 0.03em;
  text-transform: uppercase;
}
.question-nav .nav-grid {
  display: flex;
  flex-wrap: wrap;
  gap: 6px;
}
.q-nav-btn {
  width: 38px; height: 38px;
  border: 1.5px solid var(--border);
  border-radius: 8px;
  background: var(--card-bg);
  cursor: pointer;
  font-size: var(--text-sm);
  transition: all 0.15s;
  font-weight: 500;
  font-family: var(--font-ui);
  color: var(--text);
}
.q-nav-btn:hover { background: var(--primary-subtle); border-color: var(--primary); color: var(--primary); }
.q-nav-btn.current { background: var(--primary); color: #fff; border-color: var(--primary); box-shadow: 0 2px 8px rgba(37,99,235,0.25); }
.q-nav-btn.answered { border-color: var(--success); background: var(--success-light); color: #166534; }
.q-nav-btn.answered.current { background: var(--success); color: #fff; border-color: var(--success); }
.q-nav-btn.nav-correct { border-color: var(--success); background: var(--success-light); color: #166534; font-weight: 700; }
.q-nav-btn.nav-correct.current { background: var(--success); color: #fff; border-color: var(--success); }
.q-nav-btn.nav-wrong { border-color: var(--danger); background: var(--danger-light); color: #991b1b; font-weight: 700; }
.q-nav-btn.nav-wrong.current { background: var(--danger); color: #fff; border-color: var(--danger); }

.question-content {
  background: var(--card-bg);
  border-radius: var(--radius-lg);
  box-shadow: var(--shadow);
  padding: 24px 28px;
  min-height: 60vh;
  animation: fadeSlideIn 0.3s cubic-bezier(0.4, 0, 0.2, 1);
  touch-action: pan-y;
  overflow-wrap: break-word;
  word-break: break-word;
  max-width: 100%;
  overflow-x: hidden;
}
@keyframes fadeSlideIn {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}
.question-content .q-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 20px;
  padding-bottom: 14px;
  border-bottom: 1px solid var(--border);
}
.question-content .q-type {
  font-size: var(--text-xs);
  background: var(--primary-subtle);
  color: var(--primary);
  padding: 4px 12px;
  border-radius: 100px;
  font-weight: 600;
}
.question-content .q-score { font-size: var(--text-sm); color: var(--text-light); font-weight: 500; }
.question-content .q-body {
  margin: 20px 0;
  line-height: 1.85;
  max-width: 100%;
  overflow: hidden;
  font-size: var(--text-base);
  color: var(--text);
}
.question-content .q-body img { max-width: 100%; height: auto; border-radius: var(--radius-sm); }
.question-content .q-body p { margin: 10px 0; }
.question-content .q-body blockquote {
  border-left: 3px solid #d1d5db;
  padding: 8px 16px;
  color: var(--text-secondary);
  margin: 12px 0;
  background: #f8fafc;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
}

/* ===== Choice Items (Luogu-style, refined) ===== */
.choices-list { list-style: none; margin: 4px 0; }
.choices-list .choice-item {
  display: flex; align-items: flex-start; gap: 12px;
  padding: 12px 16px;
  margin: 6px 0;
  border: 1.5px solid transparent;
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all 0.15s;
  overflow-wrap: break-word;
  word-break: break-word;
  background: var(--card-bg);
}
.choices-list .choice-item:hover {
  background: var(--primary-subtle);
  border-color: var(--primary-light);
}
.choices-list .choice-item.selected {
  background: var(--primary-subtle);
  border-color: var(--primary);
}
.choices-list .choice-item.correct {
  background: var(--success-light);
  border-color: var(--success);
}
.choices-list .choice-item.wrong {
  background: var(--danger-light);
  border-color: var(--danger);
}

/* Radio circle */
.choice-radio {
  width: 22px; height: 22px;
  border-radius: 50%;
  border: 2px solid #d1d5db;
  flex-shrink: 0;
  margin-top: 1px;
  display: flex; align-items: center; justify-content: center;
  transition: all 0.2s;
}
.choice-item:hover .choice-radio { border-color: #93c5fd; }
.choice-item.selected .choice-radio {
  border-color: var(--primary);
  background: var(--primary);
}
.choice-item.selected .choice-radio::after {
  content: '';
  width: 10px; height: 10px;
  border-radius: 50%;
  background: #fff;
}
.choice-item.correct .choice-radio {
  border-color: var(--success);
  background: var(--success);
}
.choice-item.correct .choice-radio::after {
  content: '';
  width: 10px; height: 10px;
  border-radius: 50%;
  background: #fff;
}
.choice-item.wrong .choice-radio {
  border-color: var(--danger);
  background: var(--danger);
}
.choice-item.wrong .choice-radio::after {
  content: '✕';
  color: #fff;
  font-size: 11px;
  font-weight: 700;
}

/* Choice content */
.choice-content { flex: 1; min-width: 0; line-height: 1.7; font-size: var(--text-base); }
.choice-content .choice-letter {
  font-weight: 700;
  margin-right: 6px;
  color: var(--text-secondary);
  font-size: var(--text-sm);
}
.choice-item.selected .choice-letter { color: var(--primary); }
.choice-item.correct .choice-letter { color: var(--success); }
.choice-item.wrong .choice-letter { color: var(--danger); }
.choice-content p { margin: 0; display: inline; }

/* Fill-in-blank */
.blank-input {
  width: 100%;
  padding: 12px 16px;
  border: 2px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: var(--text-base);
  margin: 8px 0;
  font-family: var(--font-ui);
  transition: border-color 0.15s, box-shadow 0.15s;
  color: var(--text);
  background: var(--card-bg);
}
.blank-input:focus { border-color: var(--primary); box-shadow: 0 0 0 3px rgba(37,99,235,0.1); outline: none; }
.blank-input.correct { border-color: var(--success); background: var(--success-light); }
.blank-input.wrong { border-color: var(--danger); background: var(--danger-light); }

/* Buttons */
.btn {
  padding: 10px 22px;
  border: none;
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  cursor: pointer;
  transition: all 0.2s;
  font-family: var(--font-ui);
  font-weight: 600;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover { background: var(--primary-dark); transform: translateY(-1px); box-shadow: 0 2px 8px rgba(37,99,235,0.2); }
.btn-success { background: var(--success); color: #fff; }
.btn-success:hover { background: #15803d; transform: translateY(-1px); }
.btn-outline {
  background: transparent;
  border: 1.5px solid var(--primary);
  color: var(--primary);
  background: var(--card-bg);
}
.btn-outline:hover { background: var(--primary-subtle); transform: translateY(-1px); }
.btn-danger { background: var(--danger); color: #fff; }
.btn-danger:hover { background: #b91c1c; transform: translateY(-1px); }

.action-bar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 12px;
  margin-top: 24px;
  padding-top: 16px;
  border-top: 1px solid var(--border);
  flex-wrap: wrap;
}

/* Timer */
.timer {
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--primary);
  font-variant-numeric: tabular-nums;
  letter-spacing: 0.02em;
}
.timer.warning { color: var(--danger); animation: pulse 1s infinite; }
@keyframes pulse { 50% { opacity: 0.5; } }

/* Modal */
.modal-overlay {
  position: fixed; inset: 0;
  background: rgba(0,0,0,0.5);
  display: flex; align-items: center; justify-content: center;
  z-index: 200;
  backdrop-filter: blur(4px);
  animation: fadeIn 0.15s ease;
}
@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}
.modal {
  background: #fff;
  border-radius: var(--radius-lg);
  padding: 28px;
  width: 90%;
  max-width: 420px;
  max-height: 90vh;
  overflow-y: auto;
  box-shadow: var(--shadow-lg);
  animation: slideUp 0.2s cubic-bezier(0.4, 0, 0.2, 1);
}
@keyframes slideUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}
.modal h2 { margin-bottom: 16px; font-size: var(--text-lg); }

/* ===== Profile Modal ===== */
.profile-modal {
  max-width: 480px;
  padding: 0;
  overflow: hidden;
  border-radius: var(--radius-xl);
}
.profile-header {
  display: flex;
  align-items: center;
  gap: 16px;
  padding: 24px 28px;
  background: linear-gradient(135deg, #1e40af 0%, #3b82f6 100%);
  color: #fff;
  position: relative;
}
.profile-avatar {
  width: 52px;
  height: 52px;
  border-radius: 50%;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 1.3rem;
  font-weight: 700;
  color: #fff;
  border: 2px solid rgba(255,255,255,0.4);
  flex-shrink: 0;
}
.profile-info { flex: 1; min-width: 0; }
.profile-info h2 {
  margin: 0 0 4px;
  font-size: var(--text-lg);
  color: #fff;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.profile-info p {
  margin: 0;
  font-size: var(--text-xs);
  color: rgba(255,255,255,0.75);
}
.modal-close {
  position: absolute;
  top: 12px;
  right: 12px;
  width: 32px;
  height: 32px;
  border: none;
  border-radius: 50%;
  background: rgba(255,255,255,0.15);
  color: #fff;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: background 0.2s;
}
.modal-close:hover { background: rgba(255,255,255,0.3); }
.profile-body {
  padding: 24px 28px 20px;
}
.profile-section-title {
  font-size: var(--text-xs);
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.8px;
  margin-bottom: 14px;
}
.form-row {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 14px;
}
@media (max-width: 480px) {
  .form-row { grid-template-columns: 1fr; }
}
.profile-body .form-group label {
  display: flex;
  align-items: center;
  gap: 6px;
  font-size: var(--text-xs);
  color: var(--text-light);
  margin-bottom: 6px;
  font-weight: 500;
}
.profile-body .form-group label svg { flex-shrink: 0; }
.profile-body .form-group input,
.profile-body .form-group select {
  padding: 10px 12px;
  font-size: var(--text-sm);
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--bg);
  transition: all 0.2s;
  font-family: var(--font-ui);
  color: var(--text);
}
.profile-body .form-group input:focus,
.profile-body .form-group select:focus {
  outline: none;
  border-color: var(--primary);
  box-shadow: 0 0 0 3px rgba(37,99,235,0.1);
  background: var(--card-bg);
}
.profile-footer {
  display: flex;
  justify-content: flex-end;
  gap: 10px;
  padding: 12px 28px 24px;
}
.profile-footer .btn {
  padding: 9px 22px;
  font-size: var(--text-sm);
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.form-group { margin-bottom: 12px; }
.form-group label { display: block; font-size: 0.85rem; color: var(--text-light); margin-bottom: 4px; }
.form-group input, .form-group select {
  width: 100%; padding: 10px 12px;
  border: 1px solid var(--border);
  border-radius: var(--radius);
  font-size: 0.95rem;
}

/* Result page */
.result-summary {
  text-align: center;
  padding: 32px 24px;
  background: linear-gradient(135deg, #f0fdf4 0%, #eff6ff 100%);
  border-radius: var(--radius-lg);
}
.result-summary .big-score {
  font-size: 3.5rem;
  font-weight: 800;
  color: var(--success);
  line-height: 1.1;
  letter-spacing: -0.02em;
}
.result-summary .big-score.fail { color: var(--danger); }
.result-item {
  display: flex; align-items: center; justify-content: space-between;
  padding: 14px 18px;
  border-bottom: 1px solid var(--border);
  transition: background 0.1s;
}
.result-item:hover { background: #f8fafc; }
.result-item:last-child { border-bottom: none; }
.result-item .rn {
  font-weight: 700;
  margin-right: 10px;
  color: var(--text);
  font-size: var(--text-sm);
}
.result-item .status {
  font-size: var(--text-xs);
  padding: 4px 12px;
  border-radius: 100px;
  font-weight: 600;
}
.result-item .status.correct { background: var(--success-light); color: #166534; }
.result-item .status.wrong { background: var(--danger-light); color: #991b1b; }

/* ── Code blocks ── light theme with line numbers ── */
.q-body pre {
  background: #f6f8fa;
  border: 1px solid #d0d7de;
  border-radius: var(--radius-sm);
  padding: 16px 18px;
  overflow-x: auto;
  font-size: clamp(0.75rem, 1.5vw, 0.875rem);
  line-height: 1.65;
  margin: 16px 0;
  -webkit-overflow-scrolling: touch;
  max-width: 100%;
}
.q-body pre code {
  font-family: var(--font-mono);
  background: transparent;
  padding: 0;
  font-size: inherit;
  line-height: inherit;
  white-space: pre;
  color: #24292e;
}

/* ── highlightjs-line-numbers table styling ── */
.q-body pre table { margin: 0; padding: 0; border: none; width: auto; }
.q-body pre table tr { background: transparent !important; border: none; }
.q-body pre table tr:nth-child(even) { background: transparent !important; }
.q-body pre table td { padding: 0; border: none; vertical-align: top; text-align: left; }

.q-body pre .hljs-ln-numbers {
  text-align: right;
  color: #94a3b8 !important;
  border-right: 1px solid #d0d7de;
  padding: 0 0.8em 0 0.5em !important;
  width: 1%;
  user-select: none;
  -webkit-user-select: none;
}
.q-body pre .hljs-ln-code {
  padding: 0 0 0 1em !important;
  text-align: left;
}

/* ── Answer blanks in code: 【①】【②】... ── */
.q-body pre .code-blank,
.kp-body pre .code-blank {
  display: inline;
  background: #fff3cd;
  color: #856404;
  border: 1px solid #f0c040;
  border-radius: 4px;
  padding: 1px 6px;
  margin: 0 2px;
  font-weight: 700;
  font-size: 0.95em;
  cursor: default;
  box-shadow: 0 1px 3px rgba(0,0,0,0.08);
}

/* ── kp-body code blocks (knowledge tree) ── */
.kp-body pre table { margin: 0; padding: 0; border: none; width: auto; border-collapse: unset; }
.kp-body pre table tr { background: transparent !important; }
.kp-body pre table tr:nth-child(even) { background: transparent !important; }
.kp-body pre table td { border: none; padding: 0 4px; }
.kp-body pre table td.hljs-ln-numbers { color: #94a3b8 !important; border: none; padding-right: 8px; text-align: right; user-select: none; }
.kp-body pre table td.hljs-ln-code { border: none; padding-left: 8px; }

/* Section headers inside question body */
.q-body .q-section {
  font-size: var(--text-base);
  font-weight: 700;
  color: var(--primary);
  margin: 20px 0 10px 0;
  padding-bottom: 6px;
  border-bottom: 2px solid var(--border);
}

/* Sub-question section */
.sub-q-section {
  border-top: 1px dashed var(--border);
  padding: 16px 0;
  margin-top: 6px;
}
.sub-q-section:first-child { border-top: none; margin-top: 0; }
.sub-q-label {
  font-weight: 700;
  color: var(--primary);
  margin-bottom: 8px;
  font-size: var(--text-base);
}
.sub-q-stem {
  font-size: var(--text-sm);
  color: var(--text);
  margin-bottom: 8px;
  padding: 6px 0;
  line-height: 1.7;
}
.sub-q-score { font-weight: 400; color: var(--text-light); font-size: var(--text-xs); margin-left: 4px; }
.sub-q-info { color: var(--text-light); font-size: var(--text-xs); margin-bottom: 6px; line-height: 1.5; }

/* Answer reveal */
.reveal-answer {
  margin-top: 8px;
  padding: 8px 14px;
  border-radius: var(--radius-sm);
  font-size: var(--text-sm);
  font-weight: 600;
  display: inline-block;
}
.reveal-correct { background: var(--success-light); color: #166534; border: 1px solid #86efac; }
.reveal-wrong { background: var(--danger-light); color: #991b1b; border: 1px solid #fecaca; }


/* Images in questions */
.q-body .q-img { max-width: 100%; border-radius: var(--radius-sm); margin: 12px 0; box-shadow: var(--shadow-sm); }

/* Inline code only (not inside pre) */
.q-body > p code,
.q-body p code,
.q-body li code,
.q-body .q-section code,
.choice-content code,
.sub-q-stem code {
  font-family: var(--font-mono);
  background: #eef0f4;
  color: #d63384;
  padding: 2px 6px;
  border-radius: 4px;
  font-size: 0.88em;
}
/* Code inside code blocks stays dark */
.q-body pre.code-block code {
  font-family: var(--font-mono);
  background: transparent;
  color: inherit;
  padding: 0;
  font-size: inherit;
  line-height: inherit;
  white-space: pre;
}

/* Tables in question body */
.q-body table { border-collapse: collapse; margin: 14px 0; font-size: var(--text-sm); width: 100%; }
.q-body td, .q-body th { border: 1px solid var(--border); padding: 8px 14px; text-align: center; }
.q-body th { background: #f1f5f9; font-weight: 600; font-size: var(--text-xs); text-transform: uppercase; letter-spacing: 0.03em; }
.q-body tr:nth-child(even) { background: #f8fafc; }

/* KaTeX */
.katex-display { overflow-x: auto; overflow-y: hidden; }
.katex { font-size: 1.05em; }

/* Responsive */
@media (max-width: 767px) {
  .exam-grid { grid-template-columns: repeat(3, 1fr); }
  .mode-select { flex-direction: column; }
  .action-bar { flex-direction: column; align-items: stretch; }
  .action-bar .btn { justify-content: center; }
  .question-nav { position: static; max-height: none; }
  .question-nav .nav-grid { flex-wrap: nowrap; overflow-x: auto; }
}

/* ===== Knowledge Tree ===== */
.tree-row {
  display: flex; align-items: center; gap: 6px;
  padding: 6px 12px;
  font-size: 0.88rem;
  cursor: pointer;
  border-bottom: 1px solid #f3f4f6;
  transition: background 0.1s;
  flex-wrap: wrap;
}
.tree-row:hover { background: #f8fafc; }
.tree-folder .tree-name { font-weight: 600; color: #1e293b; }
.tree-leaf .tree-name { font-weight: 400; color: #374151; }
.tree-toggle { font-size: 0.65rem; color: #94a3b8; width: 14px; flex-shrink: 0; transition: transform 0.15s; }
.tree-dot {
  width: 8px; height: 8px; border-radius: 50%; flex-shrink: 0;
}
.tree-count { font-size: 0.7rem; color: #94a3b8; margin-left: auto; }
.tree-desc { font-size: 0.75rem; color: #9ca3af; margin-left: 8px; flex: 1; min-width: 0; overflow: hidden; text-overflow: ellipsis; white-space: nowrap; }
.tree-children.hidden { display: none; }

.diff-badge {
  font-size: 0.65rem; padding: 1px 6px; border-radius: 8px;
  color: #475569; font-weight: 600; flex-shrink: 0;
}

/* Exam filter colors */
.tree-row.tree-active { background: #f0fdf4; }
.tree-row.tree-active .tree-name { color: #166534; }
.tree-row.tree-light { background: #fefce8; }
.tree-row.tree-light .tree-name { color: #854d0e; }
.tree-row.tree-dimmed { opacity: 0.45; }
.tree-row.selected { background: #dbeafe !important; border-radius: 6px; }
.tree-row.selected .tree-name { color: #1d4ed8; font-weight: 600; }
.kp-link { color: #2563eb; cursor: pointer; text-decoration: underline; text-underline-offset: 2px; }
.kp-link:hover { color: #1d4ed8; background: #eff6ff; border-radius: 3px; }
.kp-content { font-size: 0.95rem; }
.kp-content h2 { font-size: 1.2rem; margin: 14px 0 8px; }
.kp-content h3 { font-size: 1.05rem; margin: 12px 0 6px; }
.kp-content table { width: 100%; border-collapse: collapse; margin: 8px 0; }
.kp-content th, .kp-content td { border: 1px solid #e2e8f0; padding: 6px 10px; text-align: left; font-size: 0.9rem; }
.kp-content th { background: #f8fafc; font-weight: 600; }
.kp-content pre { background: #1e293b; color: #e2e8f0; padding: 12px; border-radius: 6px; overflow-x: auto; font-size: 0.85rem; }
.kp-content code { background: #f1f5f9; padding: 2px 5px; border-radius: 3px; font-size: 0.9em; }
.kp-content pre code { background: none; padding: 0; color: inherit; }
.kp-content blockquote { border-left: 3px solid #3b82f6; margin: 8px 0; padding: 4px 12px; color: #475569; background: #f8fafc; }

/* ===== Problem Analysis Box (Redesigned for Reading Comfort) ===== */
.analysis-box {
  margin-top: 20px;
  border-top: 1px solid #e2e8f0;
  background: #fafbfc;
  border-radius: var(--radius-lg);
  padding: 16px 16px 4px;
}
.analysis-section {
  margin-bottom: 12px;
  padding: 12px 16px;
  background: #ffffff;
  border-radius: var(--radius);
  border: 1px solid var(--border);
  border-left: 4px solid #60a5fa;
  box-shadow: var(--shadow-sm);
}
.analysis-section:last-of-type { margin-bottom: 0; }
.analysis-label {
  font-weight: 700;
  font-size: 0.85rem;
  color: #1e40af;
  margin-bottom: 6px;
  display: flex;
  align-items: center;
  gap: 6px;
  letter-spacing: 0.02em;
}
.analysis-text {
  font-size: 0.95rem;
  color: #1e293b;
  line-height: 1.65;
  word-break: break-word;
  font-family: var(--font-ui);
}
.analysis-text p {
  margin: 4px 0;
}
.analysis-text p:first-child { margin-top: 0; }
.analysis-text p:last-child { margin-bottom: 0; }
.analysis-text h2 {
  font-size: 1rem;
  font-weight: 700;
  margin: 12px 0 6px;
  padding-bottom: 4px;
  border-bottom: 1px solid #e2e8f0;
  color: #1e293b;
}
.analysis-text h3 {
  font-size: 0.9rem;
  font-weight: 700;
  margin: 8px 0 4px;
  color: #334155;
}
.analysis-text h4 {
  font-size: 0.85rem;
  font-weight: 600;
  margin: 6px 0 3px;
  color: #475569;
}
.analysis-text ul,
.analysis-text ol {
  margin: 4px 0;
  padding-left: 20px;
}
.analysis-text li {
  margin: 2px 0;
}
.analysis-text table {
  font-size: 0.85rem;
  margin: 8px 0;
  border-collapse: collapse;
  width: 100%;
  border-radius: var(--radius-sm);
  overflow: hidden;
}
.analysis-text table th,
.analysis-text table td {
  border: 1px solid #d1d5db;
  padding: 6px 10px;
  text-align: center;
}
.analysis-text table th {
  background: #f1f5f9;
  font-weight: 600;
  color: #1e293b;
  font-size: 0.8rem;
  text-transform: uppercase;
  letter-spacing: 0.03em;
}
.analysis-text table tr:nth-child(even) { background: #fafbfc; }
.analysis-text pre {
  font-size: 0.85rem;
  margin: 8px 0;
  background: #f6f8fa !important;
  border: 1px solid #d0d7de !important;
  border-radius: var(--radius-sm);
  padding: 10px 14px !important;
  overflow-x: auto;
  line-height: 1.5;
}
.analysis-text pre code {
  font-family: var(--font-mono);
  font-size: 0.85rem;
  background: transparent !important;
  padding: 0 !important;
  color: #24292e;
}
/* highlightjs-line-numbers table layout inside analysis code blocks */
.analysis-text pre table { margin: 0; padding: 0; border: none; width: auto; }
.analysis-text pre table tr { background: transparent !important; border: none; }
.analysis-text pre table tr:nth-child(even) { background: transparent !important; }
.analysis-text pre table td { padding: 0; border: none; vertical-align: top; text-align: left; }
.analysis-text pre .hljs-ln-numbers {
  text-align: right;
  color: #94a3b8 !important;
  border-right: 1px solid #d0d7de;
  padding: 0 0.8em 0 0.5em !important;
  width: 1%;
  user-select: none;
}
.analysis-text pre .hljs-ln-code {
  padding: 0 0 0 1em !important;
  text-align: left;
}
.analysis-text code {
  font-family: var(--font-mono);
  font-size: 0.88em;
  background: #f1f5f9;
  color: #be123c;
  padding: 2px 6px;
  border-radius: 4px;
}
.analysis-text blockquote {
  border-left: 4px solid #3b82f6;
  margin: 8px 0;
  padding: 8px 14px;
  background: #f8fafc;
  border-radius: 0 var(--radius-sm) var(--radius-sm) 0;
  color: #475569;
  line-height: 1.6;
}
.analysis-text strong { color: #1e293b; }
.analysis-text img { max-width: 100%; height: auto; border-radius: var(--radius-sm); margin: 6px 0; }
.ai-note {
  font-size: 0.75rem;
  color: var(--text-muted);
  text-align: center;
  padding: 8px 0 2px;
  margin-top: 8px;
  border-top: 1px dashed #e2e8f0;
}
.kp-tag {
  display: inline-block;
  padding: 5px 14px;
  margin: 3px 6px 3px 0;
  background: #dbeafe;
  color: #1e40af;
  border-radius: 100px;
  font-size: var(--text-xs);
  cursor: pointer;
  transition: all 0.15s;
  font-weight: 500;
}
.kp-tag:hover { background: var(--primary); color: #fff; transform: translateY(-1px); box-shadow: 0 2px 4px rgba(37,99,235,0.2); }

.premium-locked {
  border-left-color: #f59e0b !important;
  background: linear-gradient(135deg, #fffbeb 0%, #fef3c7 100%) !important;
}
.premium-badge {
  display: inline-block;
  font-size: var(--text-xs);
  padding: 2px 8px;
  border-radius: 100px;
  background: linear-gradient(135deg, #f59e0b, #d97706);
  color: #fff;
  vertical-align: middle;
  margin-left: 6px;
  font-weight: 600;
}
.premium-placeholder {
  font-size: var(--text-sm);
  color: #92400e;
  padding: 12px;
  text-align: center;
  background: #fef3c7;
  border-radius: var(--radius-sm);
  border: 1px dashed #fbbf24;
}

/* ===== Learn Page: Two-Panel Layout ===== */
.learn-layout {
  display: flex;
  height: calc(100vh - 56px);
  overflow: hidden;
  background: var(--bg);
}
.learn-sidebar {
  width: 280px;
  min-width: 240px;
  border-right: 1px solid var(--border);
  display: flex;
  flex-direction: column;
  background: var(--card-bg);
  flex-shrink: 0;
}
.learn-sidebar-header {
  padding: 14px 16px;
  border-bottom: 1px solid var(--border);
  font-weight: 600;
  font-size: var(--text-sm);
  color: var(--text-secondary);
}
.learn-tree {
  flex: 1;
  overflow-y: auto;
  padding: 8px 0;
}
.learn-content {
  flex: 1;
  overflow-y: auto;
  background: var(--card-bg);
  padding: 28px 36px;
}

/* Tree nodes */
.tree-node {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 14px;
  cursor: pointer;
  font-size: var(--text-sm);
  line-height: 1.5;
  border-radius: 0;
  margin: 0;
  white-space: nowrap;
  transition: background 0.1s;
}
.tree-node:hover { background: var(--primary-subtle); }
.tree-node.tree-selected { background: var(--primary-light); color: var(--primary); font-weight: 600; }
.tree-dot { width: 6px; height: 6px; border-radius: 50%; display: inline-block; flex-shrink: 0; }
.tree-toggle { font-size: 0.6rem; width: 14px; text-align: center; flex-shrink: 0; color: var(--text-muted); }
.tree-label { overflow: hidden; text-overflow: ellipsis; flex: 1; }
.tree-count { font-size: var(--text-xs); color: var(--text-muted); margin-left: auto; flex-shrink: 0; }
.tree-diff { font-size: 0.625rem; padding: 0 6px; border-radius: 3px; flex-shrink: 0; font-weight: 500; background: var(--bg); color: var(--text-light); }

/* ── Article / knowledge content ── */
.kp-article { max-width: 800px; margin: 0 auto; padding: 8px 0 60px; }
.kp-article h1 {
  font-size: var(--text-2xl); font-weight: 700; color: var(--text); margin: 0 0 4px; letter-spacing: -0.01em;
  position: relative;
  display: inline-block;
}
.kp-article h1::after {
  content: '';
  position: absolute;
  left: 0; bottom: 2px;
  width: 100%; height: 10px;
  background: linear-gradient(90deg, #fde68a 0%, #fef08a 50%, #fde68a 100%);
  opacity: 0.35;
  z-index: -1;
  border-radius: 2px;
}
.kp-desc { color: var(--text-light); font-size: var(--text-sm); margin: 4px 0 14px; line-height: 1.6; }
.kp-difficulty {
  display: inline-block;
  font-size: var(--text-xs);
  padding: 4px 14px;
  border-radius: 100px;
  margin-bottom: 16px;
  font-weight: 600;
  color: #5c3d00;
  /* 荧光笔高亮效果 */
  border: 1.5px solid #eab30840;
  box-shadow: 0 1px 3px rgba(0,0,0,0.06);
}

.kp-prereqs, .kp-related {
  padding: 14px 18px;
  border-radius: var(--radius);
  margin-bottom: 16px;
  font-size: var(--text-sm);
  line-height: 1.7;
}
.kp-prereqs { background: #fffbeb; border: 1px solid #fde68a; color: #92400e; }
.kp-related { background: #f0f9ff; border: 1px solid #bae6fd; color: #1e40af; }
.kp-ref { color: var(--primary); cursor: pointer; font-weight: 500; white-space: nowrap; }
.kp-ref:hover { text-decoration: underline; }

.kp-children { margin: 20px 0; }
.kp-children h3 { font-size: var(--text-sm); font-weight: 600; color: var(--text-secondary); margin: 0 0 12px; }
.kp-children-grid { display: flex; flex-wrap: wrap; gap: 10px; }
.kp-child-card {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 10px 18px;
  background: var(--card-bg);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  font-size: var(--text-sm);
  font-weight: 500;
  color: #1e293b;
  cursor: pointer;
  transition: all 0.15s;
  text-decoration: none;
  box-shadow: 0 1px 2px rgba(0,0,0,0.04);
}
.kp-child-card:hover {
  border-color: #3b82f6;
  background: #eff6ff;
  box-shadow: 0 2px 8px rgba(59,130,246,0.15);
  transform: translateY(-1px);
  color: #1d4ed8;
}
.kp-child-card strong {
  font-weight: 600;
  color: inherit;
}
.kp-child-diff {
  font-size: 0.72rem;
  padding: 1px 7px;
  border-radius: 8px;
  background: #f1f5f9;
  color: #64748b;
  font-weight: 500;
  flex-shrink: 0;
}

/* ── Body typography ── */
.kp-body { margin: 20px 0; font-size: var(--text-base); line-height: 1.88; color: #1e293b; }
.kp-body h2 {
  font-size: var(--text-xl); font-weight: 700; color: var(--text); margin: 28px 0 12px; padding: 4px 12px;
  border-left: 4px solid #f59e0b;
  background: linear-gradient(90deg, #fffbeb 0%, transparent 100%);
  border-radius: 0 4px 4px 0;
}
.kp-body h3 {
  font-size: var(--text-lg); font-weight: 700; color: var(--text); margin: 22px 0 8px;
  padding: 2px 0 2px 10px;
  border-left: 3px solid #3b82f6;
}
.kp-body h4 {
  font-size: var(--text-base); font-weight: 600; color: var(--text-secondary); margin: 16px 0 6px;
  padding: 2px 0 2px 8px;
  border-left: 2px solid #a78bfa;
}
.kp-body p { margin: 10px 0; color: #1e293b; }
.kp-body ul, .kp-body ol { margin: 8px 0; padding-left: 24px; }
.kp-body li { margin: 4px 0; color: #1e293b; }
.kp-body strong { color: #0f172a; }

/* Tables in body */
.kp-body table { width: 100%; border-collapse: collapse; margin: 14px 0; font-size: var(--text-sm); }
.kp-body thead th { background: #f1f5f9; color: #1e293b; font-weight: 600; text-align: left; padding: 10px 12px; border: 1px solid var(--border); font-size: var(--text-xs); text-transform: uppercase; letter-spacing: 0.03em; }
.kp-body tbody td { padding: 9px 12px; border: 1px solid var(--border); color: #1e293b; }
.kp-body tbody tr:nth-child(even) { background: #fafbfc; }
.kp-body tbody tr:hover { background: #f0f9ff; }

/* Code */
.kp-body code { background: #fef9c3; color: #a21caf; padding: 2px 6px; border-radius: 4px; font-size: 0.88em; font-family: var(--font-mono); border: 1px solid #fde68a; }
.kp-body pre { background: #fefce8; color: #1c1917; padding: 16px 18px; border-radius: var(--radius-sm); overflow-x: auto; font-size: var(--text-sm); line-height: 1.65; margin: 14px 0; border: 1px solid #fde68a; box-shadow: 0 1px 4px rgba(0,0,0,0.04); }
.kp-body pre code { background: none; color: inherit; padding: 0; font-size: inherit; border: none; }
/* 代码示例标题 */
.kp-body h2:has(> .code-section-label) { border-left-color: #10b981; background: linear-gradient(90deg, #ecfdf5 0%, transparent 100%); }

/* 内联表格样式强化 */
.kp-body table { background: white; box-shadow: 0 1px 3px rgba(0,0,0,0.04); }
.kp-body table th { background: #fffbeb !important; }

/* Images in knowledge body */
.kp-body img {
  max-width: 100%;
  height: auto;
  border-radius: 8px;
  margin: 12px auto;
  display: block;
  box-shadow: 0 2px 8px rgba(0,0,0,0.08);
}
.kp-body p > img + em,
.kp-body p em:only-child {
  display: block;
  text-align: center;
  color: var(--text-light);
  font-size: 0.85rem;
  margin: -4px 0 16px;
}

/* Mermaid diagrams in knowledge content — replace pre styling with clean diagram rendering */
.kp-body .mermaid {
  background: transparent;
  margin: 16px auto;
  padding: 8px;
  text-align: center;
  overflow-x: auto;
  min-height: 60px;
}
.kp-body .mermaid svg {
  max-width: 100%;
  height: auto;
}
.kp-body .mermaid[data-processed] {
  background: #fafbfc;
  border-radius: 8px;
  border: 1px solid #e5e7eb;
}

/* Mermaid fullscreen wrapper */
.mermaid-fs-wrap { margin: 16px 0; position: relative; }
.mermaid-fs-toolbar { display: flex; justify-content: flex-end; padding: 4px 4px 0; }
.mermaid-fs-btn {
  display: inline-flex; align-items: center; gap: 3px;
  padding: 3px 10px; font-size: 0.75rem; color: #64748b;
  background: #f1f5f9; border: 1px solid #e2e8f0; border-radius: 4px;
  cursor: pointer; transition: all .15s;
}
.mermaid-fs-btn:hover { background: #e2e8f0; color: #1e293b; border-color: #94a3b8; }

/* Fullscreen overlay — pure diagram, no chrome */
.mermaid-fs-overlay {
  position: fixed; inset: 0; z-index: 9999;
  background: rgba(0,0,0,0.75); backdrop-filter: blur(6px);
  display: flex; align-items: center; justify-content: center;
  opacity: 0; transition: opacity .2s; pointer-events: none;
}
.mermaid-fs-overlay.active { opacity: 1; pointer-events: auto; }
.mermaid-fs-diagram { display: flex; align-items: center; justify-content: center; width: 100vw; height: 100vh; padding: 40px; }
.mermaid-fs-diagram svg { max-width: 100%; max-height: 95vh; height: auto; }
.mermaid-fs-close {
  position: fixed; top: 16px; right: 16px; z-index: 10000;
  background: rgba(255,255,255,0.15); border: none; border-radius: 50%;
  width: 40px; height: 40px; font-size: 1.2rem; cursor: pointer;
  display: flex; align-items: center; justify-content: center;
  color: rgba(255,255,255,0.8); transition: all .15s;
}
.mermaid-fs-close:hover { background: rgba(255,255,255,0.3); color: #fff; }

@media (prefers-color-scheme: dark) {
  .mermaid-fs-btn { background: #1e293b; color: #94a3b8; border-color: #334155; }
  .mermaid-fs-btn:hover { background: #334155; color: #e2e8f0; }
}

/* Blockquotes / callouts */
.kp-body blockquote {
  border-left: 4px solid #f59e0b;
  margin: 16px 0;
  padding: 12px 18px;
  background: #fffbeb;
  border-radius: 4px 8px 8px 4px;
  color: #78350f;
  font-size: 0.9rem;
  box-shadow: 0 1px 3px rgba(0,0,0,0.05);
  position: relative;
}
.kp-body blockquote strong { color: #92400e; }
.kp-body blockquote::before {
  content: '📝 ';
  font-size: 0.85rem;
}
/* 带 note/warning 标记的 blockquote */
.kp-body blockquote.warning { border-left-color: #ef4444; background: #fef2f2; color: #991b1b; }
.kp-body blockquote.warning strong { color: #b91c1c; }
.kp-body blockquote.tip { border-left-color: #10b981; background: #ecfdf5; color: #065f46; }
.kp-body blockquote.tip strong { color: #047857; }

.kp-empty { color: #9ca3af; padding: 60px 20px; text-align: center; font-size: 0.9rem; }

/* ── In-page TOC ── */
.kp-toc {
  background: #f8fafc;
  border: 1px solid #e2e8f0;
  border-radius: 10px;
  padding: 14px 18px;
  margin: 20px 0 8px;
  font-size: 0.88rem;
}
.kp-toc strong { color: #334155; }
.kp-toc ul { list-style: none; margin: 8px 0 0; padding: 0; }
.kp-toc li { margin: 4px 0; }
.kp-toc-link { color: #2563eb; cursor: pointer; text-decoration: none; font-size: 0.85rem; }
.kp-toc-link:hover { text-decoration: underline; color: #1d4ed8; }

/* ── Collapsed problem card ── */
.kp-problem-collapsed .kp-problem-body { padding: 12px 18px; }
.kp-problem-collapsed .kp-problem-desc { font-size: 0.85rem; line-height: 1.6; color: #64748b; margin-bottom: 10px; max-height: 4.8em; overflow: hidden; }
.kp-expand-btn { font-size: 0.82rem; padding: 6px 14px; margin-top: 4px; }
.kp-expanded-content { margin-top: 12px; padding-top: 12px; border-top: 1px dashed #e2e8f0; }

/* ── Exam analysis excerpts ── */
.kp-analysis-excerpts { margin-top: 36px; }
.kp-analysis-header { margin-bottom: 14px; }
.kp-analysis-header h3 { font-size: 1.1rem; font-weight: 700; color: #1e293b; margin: 0 0 4px; }
.kp-analysis-desc { font-size: 0.83rem; color: #64748b; margin: 0; }
.kp-analysis-item { margin-bottom: 10px; border: 1px solid #e2e8f0; border-radius: 8px; overflow: hidden; }
.kp-analysis-item[open] { border-color: #93c5fd; background: #fafbfc; }
.kp-analysis-summary { padding: 10px 14px; cursor: pointer; font-size: 0.88rem; font-weight: 600; color: #1e40af; background: #f8fafc; list-style: none; display: flex; align-items: center; gap: 6px; }
.kp-analysis-summary::-webkit-details-marker { display: none; }
.kp-analysis-summary::before { content: '▶'; font-size: 0.75rem; color: #94a3b8; transition: transform .15s; }
.kp-analysis-item[open] .kp-analysis-summary::before { content: '▼'; }
.kp-analysis-item[open] .kp-analysis-summary { border-bottom: 1px solid #e2e8f0; background: #eff6ff; }
.kp-analysis-body { padding: 12px 16px; font-size: 0.88rem; line-height: 1.7; color: #334155; }
.kp-analysis-body p { margin: 0 0 8px; color: #475569; font-size: 0.87rem; }
.kp-analysis-body p:last-child { margin-bottom: 0; }
/* Dark mode */
@media (prefers-color-scheme: dark) {
  .kp-analysis-header h3 { color: #e2e8f0; }
  .kp-analysis-desc { color: #94a3b8; }
  .kp-analysis-item { border-color: #334155; }
  .kp-analysis-item[open] { border-color: #3b82f6; background: #1e293b; }
  .kp-analysis-summary { background: #0f172a; color: #60a5fa; }
  .kp-analysis-item[open] .kp-analysis-summary { background: #1e3a5f; border-color: #334155; }
  .kp-analysis-body { color: #cbd5e1; }
  .kp-analysis-body p { color: #94a3b8; }
}

/* ── Problems section ── */
.kp-problems { margin-top: 40px; }
.kp-problems > h2 { font-size: 1.25rem; font-weight: 700; color: #111827; margin: 0 0 18px; padding-bottom: 10px; border-bottom: 2px solid #e5e7eb; }

/* Compact problem list in knowledge learning */
.kp-problem-list-compact {
  border: 1px solid #e5e7eb;
  border-radius: 8px;
  overflow: hidden;
}
.kp-problem-compact {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 10px 14px;
  border-bottom: 1px solid #f3f4f6;
  font-size: 0.85rem;
}
.kp-problem-compact:last-child { border-bottom: none; }
.kp-problem-compact:hover { background: #f9fafb; }
.kp-compact-exam {
  font-weight: 600;
  color: #2563eb;
  font-size: 0.78rem;
  white-space: nowrap;
  min-width: 80px;
}
.kp-compact-num {
  color: #6b7280;
  font-size: 0.78rem;
  white-space: nowrap;
  min-width: 50px;
}
.kp-compact-desc {
  color: #374151;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.kp-start-practice-btn {
  flex-shrink: 0;
}

.kp-problem { margin-bottom: 24px; background: #fff; border: 1px solid #e5e7eb; border-radius: 10px; overflow: hidden; transition: box-shadow 0.15s; }
.kp-problem:hover { box-shadow: 0 2px 8px rgba(0,0,0,0.04); }
.kp-problem-header { display: flex; align-items: center; gap: 10px; padding: 14px 18px; background: #f9fafb; border-bottom: 1px solid #f0f0f0; }
.kp-problem-num { display: inline-flex; align-items: center; justify-content: center; width: 28px; height: 28px; background: #2563eb; color: #fff; border-radius: 50%; font-size: 0.8rem; font-weight: 700; flex-shrink: 0; }
.kp-problem-meta { flex: 1; min-width: 0; }
.kp-problem-meta strong { font-size: 0.92rem; color: #111827; }
.kp-problem-meta span { font-size: 0.78rem; color: #6b7280; margin-left: 8px; }
.kp-problem-body { padding: 16px 18px; }
.kp-problem-desc { font-size: 0.9rem; line-height: 1.78; color: #374151; }

/* Sub-questions */
.kp-subquestions { margin-top: 12px; }
.kp-sq { margin: 12px 0; padding: 14px 16px; background: #fafbfc; border-radius: 8px; border: 1px solid #e5e7eb; }
.kp-sq-info { font-weight: 600; color: #1e293b; margin: 0 0 8px; font-size: 0.9rem; }

/* Choices - show like practice mode (interactive) */
.kp-choices { display: flex; flex-direction: column; gap: 6px; margin: 8px 0; }
.kp-choice { display: flex; align-items: flex-start; gap: 10px; padding: 10px 14px; background: #fff; border: 1.5px solid #e5e7eb; border-radius: 8px; font-size: 0.9rem; line-height: 1.6; transition: all 0.1s; }
.kp-choice:hover { border-color: #93c5fd; background: #fafcff; }
.kp-choice-label { font-weight: 700; color: #2563eb; min-width: 22px; font-size: 0.88rem; flex-shrink: 0; }
.kp-choice-text { flex: 1; min-width: 0; }

/* Clickable choice states */
.kp-choice-clickable { cursor: pointer; user-select: none; }
.kp-choice-clickable:hover { border-color: #93c5fd; background: #eff6ff; }
.kp-choice-clickable.kp-choice-selected { border-color: #2563eb; background: #dbeafe; }
.kp-choice-clickable.kp-choice-correct { border-color: #16a34a; background: #dcfce7; pointer-events: none; }
.kp-choice-clickable.kp-choice-wrong { border-color: #dc2626; background: #fef2f2; pointer-events: none; }

/* Result badge */
.kp-result-badge { display: inline-block; padding: 4px 12px; border-radius: 6px; font-size: 0.85rem; font-weight: 600; }
.kp-result-badge.correct { background: #dcfce7; color: #166534; }
.kp-result-badge.wrong { background: #fef2f2; color: #991b1b; }

/* Inline analysis in learn page */
.kp-inline-analysis { padding: 4px 0; }
.kp-inline-analysis .ana-section { margin-bottom: 8px; }

/* Answer reveal */
.kp-answer { margin-top: 10px; padding: 10px 14px; background: linear-gradient(135deg, #f0fdf4, #ecfdf5); border: 1px solid #86efac; border-radius: 8px; font-size: 0.88rem; color: #166534; }
.kp-answer strong { color: #15803d; }
.kp-judge-type { font-size: 0.75rem; color: #6b7280; margin-left: 6px; }

/* Analysis */
.kp-analysis-placeholder { margin-top: 12px; }
.kp-analysis-placeholder .btn { font-size: 0.82rem; padding: 6px 14px; }
.ana-section { margin-bottom: 10px; padding: 12px 14px; background: #fff; border-radius: 6px; border: 1px solid #e5e7eb; border-left: 4px solid #3b82f6; font-size: 0.88rem; line-height: 1.7; }
.ana-section strong { display: block; margin-bottom: 4px; color: #1e40af; font-size: 0.85rem; }

.learn-loading { display: flex; align-items: center; justify-content: center; height: 200px; color: #9ca3af; }
.learn-welcome { display: flex; flex-direction: column; align-items: center; justify-content: center; height: 100%; color: #6b7280; text-align: center; }
.learn-welcome h2 { font-size: 1.5rem; font-weight: 700; color: #374151; margin-bottom: 10px; }
.learn-error { color: #dc2626; padding: 40px; text-align: center; }

@media (max-width: 480px) {
  .learn-layout { flex-direction: column; }
  .learn-sidebar { width: 100%; max-height: 35vh; border-right: none; border-bottom: 1px solid #e5e7eb; }
  .learn-content { padding: 16px; }
  .kp-article { padding: 0 0 40px; }
  .kp-article h1 { font-size: 1.4rem; }
}

@media (max-width: 680px) {
  .tab-label { display: none; }
  .tab-icon { display: inline; font-size: 1.2rem; }
  .main-tab-link { padding: 6px 10px; }
  .main-tabs { gap: 0; }
  .app-header h1 { font-size: 0.85rem; }
  .header-brand { gap: 4px; }
  .app-header { padding: 0 6px; gap: 4px; }
  .user-name { display: none; }
  .user-profile-btn { padding: 2px 4px 2px 2px; }
  .header-actions { gap: 2px; }
  .header-icon-btn { width: 28px; height: 28px; }
}

/* ===== Dark Mode ===== */
@media (prefers-color-scheme: dark) {
  :root {
    --primary: #60a5fa;
    --primary-dark: #3b82f6;
    --primary-light: #1e3a5f;
    --primary-subtle: #1e293b;
    --success: #34d399;
    --success-light: #064e3b;
    --danger: #f87171;
    --danger-light: #4c1d1d;
    --warning: #fbbf24;
    --warning-light: #2d1a0e;
    --bg: #0f172a;
    --bg-alt: #131c31;
    --card-bg: #1e293b;
    --text: #e2e8f0;
    --text-secondary: #cbd5e1;
    --text-light: #94a3b8;
    --text-muted: #475569;
    --border: #334155;
    --border-light: #1e293b;
    --shadow-sm: 0 1px 2px rgba(0,0,0,0.2);
    --shadow: 0 1px 3px rgba(0,0,0,0.3);
    --shadow-md: 0 4px 6px -1px rgba(0,0,0,0.4);
    --shadow-lg: 0 10px 25px -5px rgba(0,0,0,0.5);
  }
  .app-header { background: linear-gradient(135deg, #0f2744 0%, #1e3a5f 100%); }
  .exam-card:hover, .exam-card:active { box-shadow: 0 4px 16px rgba(0,0,0,0.4); }
  .exam-card:hover::before { opacity: 1; }
  .pset-item:hover { background: var(--primary-subtle); }
  .question-content .q-type { background: var(--primary-light); }
  .mode-card:hover, .mode-card.selected { border-color: var(--primary); box-shadow: 0 4px 16px rgba(59,130,246,0.15); }
  .mode-card::after { background: var(--primary); }
  .q-body pre { background: #161b22; border-color: #30363d; }
  .q-body pre code { color: #c9d1d9; }
  .q-body pre .hljs-ln-numbers { color: #6e7681 !important; border-right-color: #30363d; }
  .q-body blockquote { background: var(--primary-subtle); color: var(--text-secondary); }
  .choice-item:hover { background: var(--primary-subtle); border-color: var(--primary-light); }
  .choice-item.selected { background: var(--primary-light); border-color: var(--primary); }
  .choice-item.correct { background: var(--success-light); border-color: var(--success); }
  .choice-item.wrong { background: var(--danger-light); border-color: var(--danger); }
  .choice-radio { border-color: #475569; }
  .choice-item:hover .choice-radio { border-color: #60a5fa; }
  .filter-bar select, .filter-bar input, .filter-bar button { background: var(--card-bg); color: var(--text); border-color: var(--border); }
  .kp-body pre { border-color: #475569; background: #161b22; }
  .kp-body pre code { color: #e2e8f0; }
  .kp-body pre table td { border-color: transparent; }
  .kp-body blockquote { background: #2d1a0e; color: #fbbf24; border-left-color: #f59e0b; }
  .kp-body blockquote strong { color: #fde68a; }
  .kp-body blockquote.warning { background: #4c1d1d; color: #fca5a5; border-left-color: #ef4444; }
  .kp-body blockquote.tip { background: #064e3b; color: #6ee7b7; border-left-color: #10b981; }
  .kp-content code, .kp-body code { background: #2d1a0e; color: #fca5a5; border-color: #78350f; }
  .kp-body .mermaid[data-processed] { background: var(--primary-subtle); border-color: #334155; }
  .kp-prereqs { background: #1a2e05; border-color: #4d7c0f; }
  .kp-related { background: #0c1929; border-color: var(--primary-light); }
  .kp-choice { background: var(--card-bg); border-color: #334155; }
  .kp-answer { background: var(--success-light); border-color: #065f46; color: #a7f3d0; }
  .analysis-box { background: #131c31; }
  .analysis-section { background: var(--card-bg); border-color: #334155; border-left-color: #3b82f6; }
  .analysis-text { color: var(--text-secondary); }
  .analysis-text h2 { border-bottom-color: #475569; color: var(--text); }
  .analysis-text h3 { color: var(--text-secondary); }
  .analysis-text strong { color: var(--text); }
  .analysis-text code { background: #334155; color: #fca5a5; }
  .analysis-text pre { background: #161b22 !important; border-color: #30363d !important; }
  .analysis-text pre code { color: #c9d1d9 !important; background: transparent !important; }
  .analysis-text blockquote { background: var(--primary-subtle); color: var(--text-secondary); }
  .analysis-text table th { background: #334155; color: var(--text); }
  .analysis-text table th,
  .analysis-text table td { border-color: #475569; }
  .analysis-text table tr:nth-child(even) { background: #1a2738; }
  .premium-locked {
    background: linear-gradient(135deg, #2d1a0e 0%, #3d2510 100%) !important;
    border-left-color: #f59e0b !important;
  }
  .premium-placeholder { background: #2d1a0e; color: #fbbf24; border-color: #92400e; }
  .modal { background: var(--card-bg); }
  .modal-overlay { background: rgba(0,0,0,0.7); }
  .profile-modal .profile-header { background: linear-gradient(135deg, #0f2744 0%, #1e3a5f 100%); }
  .profile-body .form-group input, .profile-body .form-group select { background: var(--bg); border-color: #334155; color: var(--text); }
  .profile-body .form-group input:focus, .profile-body .form-group select:focus { border-color: var(--primary); box-shadow: 0 0 0 3px rgba(59,130,246,0.15); background: var(--bg); }
  .form-group input, .form-group select { background: var(--bg); color: var(--text); border-color: var(--border); }
  .learn-sidebar { background: var(--bg); border-color: #334155; }
  .learn-content { background: var(--card-bg); }
  .kp-problem { background: var(--card-bg); border-color: #334155; }
  .kp-problem:hover { box-shadow: 0 2px 8px rgba(0,0,0,0.2); }
  .kp-problem-header { background: var(--bg); border-color: #334155; }
  .kp-sq { background: var(--bg); border-color: #334155; }
  .kp-children-grid .kp-child-card { background: var(--card-bg); border-color: #334155; }
  .kp-children-grid .kp-child-card:hover { border-color: var(--primary); background: var(--primary-subtle); }
  .kp-body table thead th { background: #334155; color: var(--text); }
  .kp-problem-list-compact { border-color: #334155; }
  .kp-problem-compact { border-bottom-color: var(--border-light); }
  .kp-problem-compact:hover { background: var(--primary-subtle); }
  .kp-compact-exam { color: #60a5fa; }
  .kp-compact-desc { color: var(--text-secondary); }
  .kp-body table tbody td { border-color: #334155; }
  .kp-body table tbody tr:nth-child(even) { background: #1a2738; }
  .kp-body table tbody tr:hover { background: var(--primary-subtle); }
  /* Dark mode: knowledge content highlighters */
  .kp-body h2 { background: linear-gradient(90deg, #2d1a0e 0%, transparent 100%); border-left-color: #f59e0b; }
  .kp-body h3 { border-left-color: #60a5fa; }
  .kp-body h4 { border-left-color: #a78bfa; }
  .kp-body table th { background: #2d1a0e !important; }
  .kp-body table { background: transparent; }
  .kp-article h1::after { opacity: 0.15; }
  .q-body table th { background: #334155; }
  .q-body table td { border-color: #334155; }
  .q-body table tr:nth-child(even) { background: #1a2738; }
  .sub-q-section { border-color: #334155; }
  .q-nav-btn { background: var(--card-bg); color: var(--text); border-color: var(--border); }
  .q-nav-btn:hover { background: var(--primary-subtle); border-color: var(--primary); }
  .q-nav-btn.answered { background: var(--success-light); color: #34d399; }
  .q-nav-btn.nav-correct { background: var(--success-light); color: #34d399; }
  .q-nav-btn.nav-wrong { background: var(--danger-light); color: #f87171; }
  .blank-input { background: var(--card-bg); color: var(--text); border-color: var(--border); }
  .blank-input:focus { border-color: var(--primary); box-shadow: 0 0 0 3px rgba(59,130,246,0.15); }
  .blank-input.correct { background: var(--success-light); border-color: var(--success); }
  .blank-input.wrong { background: var(--danger-light); border-color: var(--danger); }
  .reveal-correct { background: var(--success-light); color: #34d399; border-color: #065f46; }
  .reveal-wrong { background: var(--danger-light); color: #f87171; border-color: #7f1d1d; }
  .result-summary { background: linear-gradient(135deg, #064e3b 0%, #1e3a5f 100%); }
  .result-item:hover { background: var(--primary-subtle); }
  .result-item .status.correct { background: var(--success-light); color: #34d399; }
  .result-item .status.wrong { background: var(--danger-light); color: #f87171; }
  .btn-outline { background: transparent; color: var(--primary); border-color: var(--primary); }
  .btn-outline:hover { background: var(--primary-subtle); }
  .kp-tag { background: var(--primary-light); color: #93c5fd; }
  .kp-tag:hover { background: var(--primary); color: #fff; }
  .tree-row:hover { background: var(--primary-subtle); }
  .tree-node:hover { background: var(--primary-subtle); }
  .tree-node.tree-selected { background: var(--primary-light); }
  .tree-row.selected { background: var(--primary-light) !important; }
  .platform-intro { background: linear-gradient(135deg, #0a2e1a 0%, #2d1a0e 50%, #0c1929 100%); }
  .question-content .q-body blockquote { background: var(--primary-subtle); }
  .action-bar { border-top-color: var(--border); }
  .ai-note { border-top-color: #334155; }
  ::selection { background: var(--primary-light); color: #fff; }
}

/* ===== Focus visible ===== */
:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
}
button:focus-visible, a:focus-visible, .choice-item:focus-visible, .tree-node:focus-visible {
  outline: 2px solid var(--primary);
  outline-offset: 2px;
  border-radius: 4px;
}

/* ===== Skeleton Loading ===== */
@keyframes skeleton-pulse {
  0% { opacity: 0.6; }
  50% { opacity: 1; }
  100% { opacity: 0.6; }
}
.skeleton {
  background: linear-gradient(90deg, #e2e8f0 25%, #f1f5f9 50%, #e2e8f0 75%);
  background-size: 200% 100%;
  animation: skeleton-pulse 1.5s ease-in-out infinite;
  border-radius: 4px;
}
.skeleton-text { height: 14px; margin: 8px 0; width: 80%; }
.skeleton-text.short { width: 50%; }
.skeleton-title { height: 22px; margin: 12px 0; width: 60%; }
.skeleton-card { height: 80px; border-radius: 8px; margin: 8px 0; }
@media (prefers-color-scheme: dark) {
  .skeleton { background: linear-gradient(90deg, #334155 25%, #475569 50%, #334155 75%); background-size: 200% 100%; }
}

/* ===== Back to Top Button ===== */
.back-to-top {
  position: fixed;
  bottom: 24px;
  right: 24px;
  width: 44px;
  height: 44px;
  border-radius: 50%;
  background: var(--primary);
  color: #fff;
  border: none;
  cursor: pointer;
  font-size: 1.2rem;
  box-shadow: 0 2px 12px rgba(0,0,0,0.2);
  z-index: 150;
  display: none;
  align-items: center;
  justify-content: center;
  transition: transform 0.15s, opacity 0.15s;
}
.back-to-top.visible { display: flex; }
.back-to-top:hover { transform: translateY(-2px); }

/* ===== Larger touch targets ===== */
.q-nav-btn {
  min-width: 40px; min-height: 40px;
}

/* ===== Improved history modal ===== */
.history-item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 12px 14px;
  border-bottom: 1px solid var(--border);
  transition: background 0.1s;
}
.history-item:hover { background: #f8fafc; }
.history-item:last-child { border-bottom: none; }
.history-score { font-weight: 700; font-size: 0.9rem; }
.history-score.good { color: var(--success); }
.history-score.fail { color: var(--danger); }

/* ===== Empty state ===== */
.empty-state {
  text-align: center;
  padding: 40px 20px;
  color: var(--text-light);
}
.empty-state .empty-icon { font-size: 3rem; margin-bottom: 12px; }
.empty-state .empty-title { font-weight: 600; margin-bottom: 4px; color: var(--text); }

/* ===== Spinner ===== */
@keyframes spin {
  to { transform: rotate(360deg); }
}
.spinner {
  display: inline-block;
  width: 20px; height: 20px;
  border: 2px solid var(--border);
  border-top-color: var(--primary);
  border-radius: 50%;
  animation: spin 0.6s linear infinite;
  vertical-align: middle;
  margin-right: 6px;
}
.loading-text { color: var(--text-light); font-size: 0.9rem; }
.loading-text .spinner { margin-right: 8px; }

/* Utility */
.hidden { display: none !important; }
.text-center { text-align: center; }
.mt-12 { margin-top: 12px; }
.mb-12 { margin-bottom: 12px; }

/* ===== Algorithm Visualization Inline (kp-viz) ===== */
.kp-viz-section {
  margin: 24px 0 16px;
  border: 1.5px solid #d1d5db;
  border-radius: 12px;
  overflow: hidden;
  background: #fafbfc;
}
.kp-viz-section-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 12px 16px;
  background: #f1f5f9;
  border-bottom: 1px solid #e2e8f0;
  font-size: 0.92rem;
}
.kp-viz-section-icon {
  font-size: 1.1rem;
}
.kp-viz-section-header strong {
  color: #1e293b;
}
.kp-viz-section-desc {
  color: #64748b;
  font-size: 0.8rem;
  margin-left: auto;
}
.kp-viz-toggle-bar {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 14px 16px;
}
.kp-viz-hint {
  font-size: 0.78rem;
  color: #94a3b8;
}
.kp-viz-container {
  border-top: 1px solid #e2e8f0;
}
.kp-viz-empty {
  padding: 40px;
  text-align: center;
  color: #9ca3af;
}

/* Inline viz player (compact) */
.kp-viz-root {
  display: flex;
  flex-direction: column;
  background: #fff;
  font-family: 'SF Mono', 'Fira Code', 'JetBrains Mono', Menlo, monospace;
}
.kp-viz-header {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 6px 14px;
  background: #1e293b;
  color: #f1f5f9;
  font-size: 0.82rem;
}
.kp-viz-title {
  flex: 1;
  font-weight: 600;
  font-size: 0.88rem;
}
.kp-viz-step-info {
  background: #334155;
  padding: 1px 8px;
  border-radius: 4px;
  font-size: 0.75rem;
  color: #94a3b8;
}
.kp-viz-body {
  display: flex;
  min-height: 180px;
  border-bottom: 1px solid #e2e8f0;
}
.kp-viz-code-panel {
  width: 40%;
  min-width: 200px;
  display: flex;
  flex-direction: column;
  border-right: 1px solid #e2e8f0;
  background: #fafbfc;
}
.kp-viz-panel-header {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 4px 12px;
  font-size: 0.72rem;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  color: #64748b;
  background: #f1f5f9;
  border-bottom: 1px solid #e2e8f0;
  font-weight: 500;
}
.kp-viz-panel-title {
  flex-shrink: 0;
}
.kp-viz-panel-step {
  font-weight: 600;
  color: #ef4444;
  font-size: 0.68rem;
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}
.kp-viz-code-scroll {
  flex: 1;
  overflow-y: auto;
  padding: 4px 0;
  font-size: 0.75rem;
  line-height: 1.45;
  background: #f6f8fa;
}
.kv-code-line {
  display: flex;
  padding: 2px 8px 2px 10px;
  color: #24292e;
  font-family: 'Consolas', 'JetBrains Mono', 'Fira Code', monospace;
  font-size: 0.72rem;
  border-left: 3px solid transparent;
  transition: all 0.12s ease;
}
/* Section header lines (// ─── 标题 ───) */
.kv-code-line.kv-section-header {
  background: #eff6ff;
  border-left: 3px solid #3b82f6;
  border-bottom: 1px solid #d0d7de;
  padding: 4px 8px 4px 10px;
  margin-top: 4px;
}
.kv-section-text {
  font-weight: 700;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  font-size: 0.72rem;
  color: #2563eb;
  letter-spacing: 0.02em;
}
/* Highlighted code line — step's current focus */
.kv-code-line.kv-code-hl {
  background: #fef2f2;
  border-left: 3px solid #ef4444;
}
/* Active (last highlighted) line — where execution currently is */
.kv-code-line.kv-code-active {
  background: #fee2e2;
  border-left: 3px solid #dc2626;
  font-weight: 600;
}
/* Dimmed lines — not relevant in this step */
.kv-code-line.kv-code-dim {
  opacity: 0.45;
}
.kv-line-num {
  display: inline-block;
  width: 26px;
  text-align: right;
  color: #9ca3af;
  font-size: 0.7rem;
  margin-right: 10px;
  user-select: none;
  flex-shrink: 0;
  transition: color 0.12s ease;
}
.kv-line-num.kv-line-hl {
  color: #dc2626;
  font-weight: 700;
}
.kv-line-content {
  white-space: pre;
}
.kp-viz-viz-panel {
  flex: 1;
  display: flex;
  flex-direction: column;
  background: #fafbfc;
}
.kp-viz-viz-content {
  flex: 1;
  display: flex;
  flex-direction: column;
  align-items: center;
  overflow: auto;
  padding: 4px;
}
.kp-viz-svg {
  width: 100%;
  max-width: 600px;
  height: auto;
  min-height: 180px;
}
.kp-viz-svg .kv-svg-title {
  font-size: 13px;
  font-weight: 700;
  fill: #1e293b;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}
.kp-viz-svg .kv-svg-caption {
  font-size: 11px;
  fill: #64748b;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}
.kp-viz-svg .kv-bar-label {
  font-size: 10px;
  fill: #374151;
}
.kp-viz-svg .kv-bar-value {
  font-size: 9px;
  fill: #374151;
}
.kp-viz-legend {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  padding: 2px 10px 6px;
  justify-content: center;
  font-size: 0.72rem;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  color: #475569;
}
.kv-legend-item {
  display: inline-flex;
  align-items: center;
  gap: 3px;
}
.kv-legend-dot {
  display: inline-block;
  width: 8px;
  height: 8px;
  border-radius: 2px;
  flex-shrink: 0;
}
.kv-result-text {
  font-size: 22px;
  fill: #2563eb;
  font-weight: 700;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}
.kv-result-sub {
  font-size: 12px;
  fill: #6b7280;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}

/* Variables bar */
.kp-viz-vars-bar {
  background: #f8fafc;
  border-bottom: 1px solid #e2e8f0;
  max-height: 120px;
  overflow-y: auto;
}
.kp-viz-vars-scroll {
  overflow-x: auto;
  padding: 6px 12px;
}
.kv-vars-table {
  border-collapse: collapse;
  font-size: 0.72rem;
  font-family: 'SF Mono', 'Fira Code', 'Microsoft YaHei', 'PingFang SC', monospace;
  width: 100%;
}
.kv-vars-table th {
  text-align: left;
  padding: 2px 12px 2px 0;
  color: #94a3b8;
  font-weight: 500;
  font-size: 0.65rem;
  border-bottom: 1px solid #e2e8f0;
  white-space: nowrap;
}
.kv-vars-table td {
  padding: 2px 12px 2px 0;
  color: #374151;
  white-space: nowrap;
}
.kv-var-name {
  color: #3b82f6;
  font-weight: 600;
  white-space: nowrap;
}
.kv-var-val {
  max-width: 260px;
  overflow: hidden;
  text-overflow: ellipsis;
}
.kv-var-hl {
  color: #dc2626;
  font-weight: 700;
  animation: kv-pulse 0.6s ease;
}
@keyframes kv-pulse {
  0%, 100% { opacity: 1; }
  50% { opacity: 0.5; background: #fee2e2; border-radius: 2px; }
}

/* Controls */
.kp-viz-controls {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 6px;
  padding: 6px 12px;
  background: #f1f5f9;
  border-top: 1px solid #e2e8f0;
}
.kv-ctrl {
  background: transparent;
  border: 1px solid #cbd5e1;
  color: #475569;
  padding: 3px 12px;
  border-radius: 5px;
  cursor: pointer;
  font-size: 0.82rem;
  transition: all 0.15s;
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
}
.kv-ctrl:hover:not(:disabled) {
  background: #e2e8f0;
  border-color: #94a3b8;
}
.kv-ctrl:disabled {
  opacity: 0.35;
  cursor: default;
}
.kv-play-btn {
  min-width: 80px;
  background: #2563eb;
  color: #fff;
  border-color: #2563eb;
  font-size: 0.82rem;
  font-weight: 600;
}
.kv-play-btn:hover:not(:disabled) {
  background: #1d4ed8;
  border-color: #1d4ed8;
}
.kv-speed {
  margin-left: 6px;
  padding: 2px 6px;
  border: 1px solid #cbd5e1;
  border-radius: 4px;
  font-size: 0.72rem;
  background: #fff;
  color: #475569;
}

/* ===== KP Navigation ===== */
.kp-nav {
  margin: 28px 0 8px;
}
.kp-nav-inner {
  display: flex;
  justify-content: space-between;
  gap: 16px;
}
.kp-nav-prev, .kp-nav-next {
  flex: 1;
}
.kp-nav-next {
  text-align: right;
}
.kp-nav-link {
  display: inline-block;
  padding: 10px 18px;
  border: 1.5px solid #d1d5db;
  border-radius: 10px;
  font-size: 0.9rem;
  font-weight: 500;
  transition: all 0.15s;
  background: #fff;
  box-shadow: 0 1px 2px rgba(0,0,0,0.04);
}
.kp-nav-link:hover {
  border-color: #3b82f6;
  background: #eff6ff;
  box-shadow: 0 2px 8px rgba(59,130,246,0.15);
  transform: translateY(-1px);
  color: #1d4ed8;
}
.kp-up-nav {
  margin: 12px 0 24px;
  text-align: center;
  font-size: 0.85rem;
}
.kp-up-nav .kp-link {
  padding: 6px 14px;
  border-radius: 8px;
  background: #f8fafc;
  border: 1px solid #e2e8f0;
  display: inline-block;
  transition: all 0.15s;
}
.kp-up-nav .kp-link:hover {
  background: #eff6ff;
  border-color: #93c5fd;
}
.kp-viz-start-btn {
  font-size: 0.88rem;
  padding: 8px 20px;
}

/* Fullscreen mode */
.kp-viz-fullscreen {
  position: fixed !important;
  top: 0 !important;
  left: 0 !important;
  right: 0 !important;
  bottom: 0 !important;
  z-index: 99999 !important;
  width: 100vw !important;
  height: 100vh !important;
  max-width: none !important;
  max-height: none !important;
  margin: 0 !important;
  border-radius: 0 !important;
  border: none !important;
  background: #fff !important;
}
.kp-viz-fullscreen .kp-viz-body {
  flex: 1;
  min-height: 0;
  height: auto;
}
.kp-viz-fullscreen .kp-viz-code-panel {
  width: 35%;
  min-width: 260px;
}
.kp-viz-fullscreen .kp-viz-code-scroll {
  font-size: 0.82rem;
  line-height: 1.5;
}
.kp-viz-fullscreen .kv-code-line {
  font-size: 0.8rem;
  padding: 2px 10px;
}
.kp-viz-fullscreen .kp-viz-viz-content {
  padding: 8px;
}
.kp-viz-fullscreen .kp-viz-vars-bar {
  max-height: 160px;
}
.kp-viz-fullscreen .kp-viz-vars-scroll {
  padding: 8px 16px;
}
.kp-viz-fullscreen .kv-vars-table {
  font-size: 0.78rem;
}
.kp-viz-fullscreen .kp-viz-controls {
  padding: 10px 16px;
  gap: 10px;
}
.kp-viz-fullscreen .kv-ctrl {
  padding: 6px 18px;
  font-size: 0.9rem;
}
.kp-viz-fullscreen .kv-play-btn {
  min-width: 100px;
}
.kv-fullscreen-btn {
  margin-left: auto;
  font-size: 1rem;
  padding: 3px 10px !important;
  min-width: auto !important;
}

/* Dark mode overrides for inline viz */
@media (prefers-color-scheme: dark) {
  .kp-viz-section { border-color: #334155; background: #1e293b; }
  .kp-viz-section-header { background: #0f172a; border-color: #334155; }
  .kp-viz-section-header strong { color: #e2e8f0; }
  .kp-viz-root { background: #1e293b; }
  .kp-viz-header { background: #0f172a; }
  .kp-viz-code-panel { background: #0f172a; border-color: #334155; }
  .kp-viz-panel-header { background: #1e293b; color: #94a3b8; border-color: #334155; }
  .kp-viz-code-scroll { background: #0f172a; }
  .kv-code-line { color: #c9d1d9; }
  .kv-code-line.kv-code-hl { background: #2d1b1b; border-left-color: #ef4444; }
  .kv-code-line.kv-code-active { background: #3d2020; border-left-color: #dc2626; }
  .kv-code-line.kv-code-dim { opacity: 0.35; }
  .kv-code-line.kv-section-header { background: #172554; border-left-color: #3b82f6; }
  .kv-section-text { color: #60a5fa; }
  .kv-line-num.kv-line-hl { color: #ef4444; }
  .kp-viz-panel-step { color: #f87171; }
  .kp-viz-viz-panel { background: #0f172a; }
  .kp-viz-vars-bar { background: #0f172a; border-color: #334155; }
  .kv-vars-table td { color: #cbd5e1; }
  .kv-vars-table th { color: #64748b; }
  .kp-viz-controls { background: #1e293b; border-color: #334155; }
  .kv-ctrl { background: #1e293b; color: #cbd5e1; border-color: #475569; }
  .kv-ctrl:hover:not(:disabled) { background: #334155; }
  .kp-viz-svg .kv-svg-title { fill: #e2e8f0; }
  .kp-viz-svg .kv-bar-label { fill: #cbd5e1; }
  .kp-viz-svg .kv-bar-value { fill: #cbd5e1; }
  .kp-viz-svg .kv-svg-caption { fill: #94a3b8; }
  .kv-result-text { fill: #60a5fa; }
  .kv-result-sub { fill: #94a3b8; }
  .kp-nav-link { background: #1e293b; border-color: #475569; color: #cbd5e1; }
  .kp-nav-link:hover { border-color: #3b82f6; background: #1e3a5f; color: #60a5fa; }
  .kp-up-nav .kp-link { background: #1e293b; border-color: #334155; }
  .kv-speed { background: #1e293b; color: #cbd5e1; border-color: #475569; }
  .kp-viz-section-desc { color: #94a3b8; }
  .kp-viz-fullscreen .kp-viz-code-panel { background: #0f172a; border-color: #334155; }
  .kp-viz-fullscreen .kp-viz-viz-panel { background: #0f172a; }
  .kp-viz-fullscreen .kp-viz-vars-bar { background: #0f172a; border-color: #334155; }
  .kp-viz-fullscreen .kp-viz-controls { background: #1e293b; border-color: #334155; }
  .kp-viz-fullscreen .kv-vars-table td { color: #c9d1d9; }
}

/* ===== Sketchpad / 全屏半透明草稿画板 ===== */
#sketchpad-overlay {
  display: none;
  position: fixed; top: 0; left: 0; width: 100%; height: 100%;
  z-index: 10000;
  background: rgba(255,248,220,0.22); /* 淡黄色半透明，像草稿纸 */
}
#sketchpad-overlay.open {
  display: block;
}

/* Scrollable wrapper — fills the entire overlay */
#sketchpad-scroll {
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  overflow-y: auto;
  overflow-x: hidden;
}

#sketchpad-canvas {
  display: block;
  cursor: crosshair;
}

/* Floating toolbar — fixed at top center, stays when scrolling */
#sketchpad-toolbar {
  position: fixed;
  top: 16px;
  left: 50%;
  transform: translateX(-50%);
  z-index: 10001;
  padding: 8px 16px;
  background: rgba(255,255,255,0.92);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  border: 1px solid rgba(255,255,255,0.4);
  border-radius: 12px;
  box-shadow: 0 2px 12px rgba(0,0,0,0.1);
  display: flex;
  align-items: center;
  user-select: none;
}
.sketch-tools {
  display: flex;
  align-items: center;
  gap: 6px;
}
.sketch-btn {
  padding: 6px 14px;
  border: 1px solid rgba(0,0,0,0.08);
  border-radius: 8px;
  background: rgba(255,255,255,0.8);
  color: #374151;
  font-size: 0.9rem;
  cursor: pointer;
  transition: all 0.15s;
  line-height: 1.4;
  min-width: 36px;
  text-align: center;
}
.sketch-btn:hover {
  background: rgba(243,244,246,0.9);
  border-color: rgba(0,0,0,0.15);
}
.sketch-btn.active {
  background: var(--primary, #2563eb);
  color: #fff;
  border-color: var(--primary, #2563eb);
  box-shadow: 0 1px 4px rgba(37,99,235,0.3);
}
.sketch-btn-text {
  font-size: 0.82rem;
  padding: 6px 12px;
}
.sketch-sep {
  color: rgba(0,0,0,0.12);
  margin: 0 6px;
  user-select: none;
}

/* Eraser icon — pink rectangular block */
.eraser-icon {
  display: inline-block;
  width: 18px;
  height: 13px;
  background: #f9a8b4;
  border: 1.5px solid #db5a6b;
  border-radius: 2px;
  vertical-align: middle;
}

/* Size controls */
.sketch-btn-icon {
  font-size: 1.05rem;
  font-weight: 700;
  line-height: 1;
  padding: 6px 10px;
  min-width: 32px;
}
.sketch-size-indicator {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 32px;
  height: 32px;
}
.size-dot {
  display: inline-block;
  border-radius: 50%;
  background: #374151;
  transition: all 0.2s ease;
}

/* Select tool icon — dashed square */
.select-icon {
  display: inline-block;
  width: 16px;
  height: 16px;
  border: 2px dashed #555;
  border-radius: 1px;
  vertical-align: middle;
}

/* Paste button */
#sketch-paste {
  font-size: 0.85rem;
}

/* Resize handles for pasted image */
.sketch-resize-handle {
  transition: background 0.15s, transform 0.15s;
}
.sketch-resize-handle:hover {
  background: #2563eb !important;
  transform: scale(1.3);
}

/* Pasted image container */
#sketchpad-floating-img {
  transition: none;
}

/* Toast for paste feedback */
#sketch-toast {
  opacity: 0;
}

/* Selection rectangle overlay */
#sketchpad-sel-rect {
  position: absolute;
  z-index: 5;
  border: 2px dashed #2563eb;
  background: rgba(37,99,235,0.08);
  pointer-events: none;
  display: none;
}

/* Floating selection overlay canvas (during move) */
#sketchpad-sel-overlay {
  position: absolute;
  z-index: 4;
  pointer-events: none;
  display: none;
  image-rendering: auto;
}

/* Sketch trigger button in practice header */
.sketch-trigger {
  flex-shrink: 0;
}

/* ── 题单页 ── */
.pl-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); gap: 14px; }
.pl-card {
  display: block; background: #fff; border: 1px solid #e5e7eb; border-radius: 12px;
  padding: 14px 16px; text-decoration: none; color: inherit;
  transition: box-shadow .15s, transform .15s;
}
.pl-card:hover { box-shadow: 0 4px 14px rgba(0,0,0,.08); transform: translateY(-2px); }
.pl-card-name { font-weight: 600; font-size: 15px; margin-bottom: 8px; color: #1f2937; }
.pl-card-meta { display: flex; gap: 6px; flex-wrap: wrap; }
.pl-empty { text-align: center; color: #6b7280; padding: 40px 20px; }
.pl-problem-list { display: flex; flex-direction: column; gap: 10px; margin-top: 14px; }
.pl-problem-item {
  display: flex; justify-content: space-between; align-items: center; gap: 12px; flex-wrap: wrap;
  background: #fff; border: 1px solid #e5e7eb; border-radius: 12px; padding: 12px 16px;
}
.pl-problem-main { display: flex; gap: 12px; align-items: flex-start; }
.pl-problem-order {
  background: #2563eb; color: #fff; font-size: 12px; font-weight: 700;
  min-width: 22px; height: 22px; border-radius: 999px;
  display: inline-flex; align-items: center; justify-content: center;
}
.pl-problem-title { font-weight: 600; color: #1f2937; }
.pl-problem-meta { display: flex; gap: 6px; flex-wrap: wrap; margin-top: 4px; }
.pl-problem-actions { display: flex; gap: 8px; }

/* ── AI 逐题讲解 ── */
.ai-expl-wrap { margin-top: 10px; }
.ai-expl-body { margin-top: 10px; }
.ai-expl-loading { color: #64748b; font-size: 0.9rem; padding: 8px 0; }
.ai-expl-error { color: #dc2626; font-size: 0.9rem; padding: 8px 0; }
.ai-expl-box {
  border: 1px solid #bfdbfe; border-radius: 12px; background: #f8fafc;
  padding: 14px 16px; margin-top: 8px;
}
.ai-expl-head { display: flex; align-items: center; gap: 8px; flex-wrap: wrap; margin-bottom: 10px; font-weight: 700; }
.ai-expl-answer-chip { background: #dcfce7; color: #166534; }
.ai-expl-personalized {
  background: #fff7ed; border: 1px solid #fed7aa; border-radius: 10px;
  padding: 10px 14px; margin-bottom: 10px; font-size: 0.9rem; line-height: 1.7;
}
.ai-expl-section { margin-top: 10px; }
.ai-expl-section-title { font-weight: 600; font-size: 0.9rem; color: #334155; margin-bottom: 6px; }
.ai-expl-option {
  border: 1px solid #e5e7eb; border-radius: 10px; padding: 8px 12px; margin-bottom: 8px;
  background: #fff;
}
.ai-expl-option.correct { border-color: #86efac; background: #f0fdf4; }
.ai-expl-option.wrong { border-color: #fca5a5; background: #fef2f2; }
.ai-expl-option-head { display: flex; align-items: center; gap: 6px; font-weight: 600; }
.ai-expl-option-mark { font-weight: 700; }
.ai-expl-option.correct .ai-expl-option-mark { color: #16a34a; }
.ai-expl-option.wrong .ai-expl-option-mark { color: #dc2626; }
.ai-expl-option-analysis { margin-top: 4px; font-size: 0.88rem; color: #475569; line-height: 1.7; }
.ai-expl-reasoning { font-size: 0.9rem; color: #1f2937; line-height: 1.8; }
.ai-expl-summary { background: #eff6ff; border-radius: 8px; padding: 8px 12px; font-size: 0.88rem; color: #1e3a8a; }

/* ── 题单搜索 ── */
.pl-search-input {
  padding: 6px 12px; border-radius: 8px; border: 1px solid #d0d7de;
  font-size: 14px; min-width: 200px; outline: none;
}
.pl-search-input:focus { border-color: #2563eb; box-shadow: 0 0 0 2px rgba(37,99,235,.12); }