/* ── Fonts ─────────────────────────────────────────────── */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@300;400;500;600;700&display=swap');

/* ── Design Tokens ─────────────────────────────────────── */
:root {
  --bg:             #F0F2FA;
  --surface:        #FFFFFF;
  --surface-2:      #F5F7FD;
  --primary:        #6875C8;
  --primary-dark:   #4A56A8;
  --primary-light:  #EEF0FC;
  --accent:         #9B8EC4;
  --text:           #1E2240;
  --text-muted:     #6B6F8A;
  --border:         #DDE1F0;
  --border-strong:  #BEC4E0;
  --correct-bg:     #EEF5F1;
  --correct-border: #5B8A6F;
  --correct-text:   #3A6B4E;
  --wrong-bg:       #F9EEEE;
  --wrong-border:   #B85C5C;
  --wrong-text:     #8A3A3A;
  --radius:         10px;
  --radius-sm:      6px;
  --shadow:         0 2px 12px rgba(104,117,200,0.08);
  --shadow-md:      0 4px 24px rgba(104,117,200,0.12);
  --transition:     0.18s ease;
}

/* ── Reset ─────────────────────────────────────────────── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { -webkit-font-smoothing: antialiased; }
body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.6;
  min-height: 100vh;
}
a { color: var(--primary); text-decoration: none; }
a:hover { color: var(--primary-dark); }
button { cursor: pointer; font-family: inherit; }

/* ── Header ─────────────────────────────────────────────── */
.site-header {
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 0 2rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 58px;
  position: sticky;
  top: 0;
  z-index: 100;
  box-shadow: var(--shadow);
}
.site-header .logo {
  font-size: 1rem;
  font-weight: 700;
  color: var(--primary);
  letter-spacing: -0.3px;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.site-header .logo span { color: var(--text); font-weight: 400; }
.breadcrumb {
  font-size: 0.82rem;
  color: var(--text-muted);
  display: flex;
  align-items: center;
  gap: 0.4rem;
}
.breadcrumb a { color: var(--text-muted); }
.breadcrumb a:hover { color: var(--primary); }

/* ── Index: Course Cards ────────────────────────────────── */
.index-hero {
  text-align: center;
  padding: 3.5rem 2rem 2rem;
}
.index-hero h1 {
  font-size: 1.8rem;
  font-weight: 700;
  color: var(--text);
  margin-bottom: 0.5rem;
}
.index-hero p {
  font-size: 0.95rem;
  color: var(--text-muted);
}
.course-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(280px, 1fr));
  gap: 1.2rem;
  max-width: 960px;
  margin: 2rem auto;
  padding: 0 1.5rem;
}
.course-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 1.4rem 1.6rem;
  box-shadow: var(--shadow);
  cursor: pointer;
  transition: box-shadow var(--transition), transform var(--transition), border-color var(--transition);
  text-decoration: none;
  display: block;
}
.course-card:hover {
  box-shadow: var(--shadow-md);
  border-color: var(--primary);
  transform: translateY(-2px);
}
.course-card .course-id {
  font-size: 0.72rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--primary);
  background: var(--primary-light);
  display: inline-block;
  padding: 0.2rem 0.55rem;
  border-radius: 4px;
  margin-bottom: 0.7rem;
}
.course-card h2 {
  font-size: 1.05rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.35rem;
}
.course-card p {
  font-size: 0.85rem;
  color: var(--text-muted);
  line-height: 1.5;
}
.course-card .module-pills {
  display: flex;
  flex-wrap: wrap;
  gap: 0.35rem;
  margin-top: 1rem;
}
.module-pill {
  font-size: 0.72rem;
  padding: 0.18rem 0.6rem;
  border-radius: 20px;
  background: var(--bg);
  border: 1px solid var(--border);
  color: var(--text-muted);
  font-weight: 500;
}

/* ── Course Page Layout ─────────────────────────────────── */
.course-layout {
  max-width: 1100px;
  margin: 0 auto;
  padding: 1.5rem;
}
.course-title {
  margin-bottom: 1.5rem;
}
.course-title h1 {
  font-size: 1.35rem;
  font-weight: 700;
}
.course-title p {
  font-size: 0.85rem;
  color: var(--text-muted);
  margin-top: 0.15rem;
}

/* ── Primary Tabs ───────────────────────────────────────── */
.tab-bar {
  display: flex;
  gap: 0.2rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.3rem;
  width: fit-content;
  margin-bottom: 1.2rem;
}
.tab-btn {
  padding: 0.45rem 1.2rem;
  border: none;
  background: none;
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-weight: 500;
  color: var(--text-muted);
  transition: background var(--transition), color var(--transition);
}
.tab-btn.active {
  background: var(--primary);
  color: #fff;
  font-weight: 600;
}
.tab-btn:hover:not(.active) {
  background: var(--primary-light);
  color: var(--primary);
}

/* ── Module Filter Bar ──────────────────────────────────── */
.filter-bar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 1.2rem;
}
.filter-label {
  font-size: 0.78rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-right: 0.2rem;
}
.filter-btn {
  padding: 0.3rem 0.85rem;
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: 20px;
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--text-muted);
  transition: all var(--transition);
}
.filter-btn:hover { border-color: var(--primary); color: var(--primary); }
.filter-btn.active {
  background: var(--primary);
  border-color: var(--primary);
  color: #fff;
}

/* ── Mode Selector ──────────────────────────────────────── */
#mode-selector {
  display: flex;
  flex-direction: column;
  gap: 0.45rem;
  margin-bottom: 1.2rem;
}
.mode-row {
  display: flex;
  align-items: center;
  gap: 0.35rem;
  flex-wrap: wrap;
}
.mode-btn {
  padding: 0.38rem 1rem;
  border: 1px solid var(--border);
  background: var(--surface);
  border-radius: 20px;
  font-size: 0.82rem;
  font-weight: 500;
  color: var(--text-muted);
  transition: all var(--transition);
}
.mode-btn:hover { border-color: var(--accent); color: var(--accent); }
.mode-btn.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

/* ── Score Bar ──────────────────────────────────────────── */
.score-bar {
  display: flex;
  align-items: center;
  gap: 1rem;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 0.7rem 1.2rem;
  margin-bottom: 1.2rem;
  font-size: 0.88rem;
  box-shadow: var(--shadow);
}
.score-bar .score-num {
  font-weight: 700;
  font-size: 1.1rem;
  color: var(--primary);
}
.score-bar .score-label { color: var(--text-muted); }
.score-progress {
  flex: 1;
  height: 6px;
  background: var(--border);
  border-radius: 4px;
  overflow: hidden;
}
.score-progress-fill {
  height: 100%;
  background: linear-gradient(90deg, var(--primary), var(--accent));
  border-radius: 4px;
  transition: width 0.4s ease;
}

/* ── Question Card ──────────────────────────────────────── */
.question-list { display: flex; flex-direction: column; gap: 1rem; }
.q-card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  overflow: hidden;
  transition: border-color var(--transition);
}
.q-card.answered-correct { border-color: var(--correct-border); }
.q-card.answered-wrong   { border-color: var(--wrong-border); }

.q-card-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.8rem 1.2rem;
  background: var(--surface-2);
  border-bottom: 1px solid var(--border);
}
.q-meta { display: flex; align-items: center; gap: 0.5rem; }
.q-badge {
  font-size: 0.68rem;
  font-weight: 600;
  letter-spacing: 0.05em;
  text-transform: uppercase;
  padding: 0.18rem 0.55rem;
  border-radius: 4px;
}
.q-badge.single   { background: #EEF0FC; color: var(--primary); }
.q-badge.matching { background: #F0F5EE; color: #4A7A5A; }
.q-badge.causal   { background: #F5F0EE; color: #7A4A3A; }

.q-num {
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--text-muted);
}
.q-source-badge {
  font-size: 0.75rem;
  color: var(--text-muted);
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  padding: 0.2rem 0.6rem;
  border: 1px solid var(--border);
  border-radius: 20px;
  user-select: none;
}

.q-card-body { padding: 1.2rem; }
.q-topic {
  font-size: 0.73rem;
  font-weight: 600;
  color: var(--accent);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  margin-bottom: 0.5rem;
}
.q-text {
  font-size: 0.95rem;
  line-height: 1.65;
  color: var(--text);
  margin-bottom: 1rem;
}

/* ── Single Choice ──────────────────────────────────────── */
.choices { display: flex; flex-direction: column; gap: 0.45rem; }
.choice-item {
  display: flex;
  align-items: flex-start;
  gap: 0.7rem;
  padding: 0.6rem 0.9rem;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition);
  user-select: none;
}
.choice-item:hover   { border-color: var(--primary); background: var(--primary-light); }
.choice-item.selected{ border-color: var(--primary); background: var(--primary-light); }
.choice-item.correct { border-color: var(--correct-border); background: var(--correct-bg); }
.choice-item.wrong   { border-color: var(--wrong-border);   background: var(--wrong-bg); }
.choice-item.dim     { opacity: 0.4; pointer-events: none; }
.choice-letter {
  font-weight: 700;
  font-size: 0.85rem;
  color: var(--primary);
  min-width: 1.5rem;
  line-height: 1.5;
}
.choice-text { font-size: 0.9rem; line-height: 1.5; flex: 1; }

/* ── Matching Sets ──────────────────────────────────────── */
.matching-instructions {
  font-size: 0.85rem;
  color: var(--text-muted);
  font-style: italic;
  margin-bottom: 0.8rem;
  padding: 0.6rem 0.8rem;
  background: var(--surface-2);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--accent);
}
.matching-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 0.5rem; }
@media (max-width: 600px) { .matching-grid { grid-template-columns: 1fr; } }
.matching-row {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  padding: 0.5rem 0.7rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  background: var(--surface-2);
}
.matching-row.correct-match { border-color: var(--correct-border); background: var(--correct-bg); }
.matching-row.wrong-match   { border-color: var(--wrong-border);   background: var(--wrong-bg); }
.matching-num {
  font-weight: 700;
  font-size: 0.85rem;
  color: var(--primary);
  min-width: 1.4rem;
}
.matching-item-text { font-size: 0.88rem; flex: 1; line-height: 1.4; }
.matching-select {
  padding: 0.25rem 0.5rem;
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
  font-family: inherit;
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
  min-width: 50px;
}

/* ── Causal Relationship ────────────────────────────────── */
.causal-statement {
  font-size: 0.92rem;
  line-height: 1.65;
  padding: 0.8rem 1rem;
  background: var(--surface-2);
  border-radius: var(--radius-sm);
  border-left: 3px solid var(--accent);
  margin-bottom: 1rem;
}
.causal-statement .because  { font-weight: 600; color: var(--primary); }
.causal-statement .therefore{ font-weight: 600; color: var(--accent); }
.causal-options { display: flex; flex-direction: column; gap: 0.4rem; }
.causal-option {
  display: flex;
  align-items: flex-start;
  gap: 0.7rem;
  padding: 0.55rem 0.9rem;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  cursor: pointer;
  transition: all var(--transition);
  user-select: none;
}
.causal-option:hover   { border-color: var(--accent); background: #F5F0FF; }
.causal-option.selected{ border-color: var(--accent); background: #F5F0FF; }
.causal-option.correct { border-color: var(--correct-border); background: var(--correct-bg); }
.causal-option.wrong   { border-color: var(--wrong-border);   background: var(--wrong-bg); }
.causal-option.dim     { opacity: 0.4; pointer-events: none; }
.causal-num {
  font-weight: 700;
  font-size: 0.82rem;
  color: var(--accent);
  min-width: 1.5rem;
}
.causal-text { font-size: 0.88rem; line-height: 1.5; flex: 1; }

/* ── Answer Reveal ──────────────────────────────────────── */
.answer-panel {
  display: none;
  margin-top: 1rem;
  padding: 0.9rem 1rem;
  border-radius: var(--radius-sm);
  border-left: 4px solid var(--correct-border);
  background: var(--correct-bg);
  font-size: 0.88rem;
  line-height: 1.6;
}
.answer-panel.visible { display: block; }
.answer-panel.wrong-reveal { border-color: var(--primary); background: var(--primary-light); }
.answer-panel strong { color: var(--correct-text); }
.answer-panel .explanation { color: var(--text); margin-top: 0.4rem; }

/* ── Action Buttons ─────────────────────────────────────── */
.q-actions {
  display: flex;
  align-items: center;
  gap: 0.6rem;
  margin-top: 1rem;
  padding-top: 0.8rem;
  border-top: 1px solid var(--border);
}
.btn-check {
  padding: 0.45rem 1.1rem;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 0.85rem;
  font-weight: 600;
  transition: background var(--transition);
}
.btn-check:hover { background: var(--primary-dark); }
.btn-check:disabled { background: var(--border); color: var(--text-muted); cursor: not-allowed; }
.btn-reset {
  padding: 0.45rem 0.9rem;
  background: none;
  color: var(--text-muted);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 0.82rem;
  transition: all var(--transition);
}
.btn-reset:hover { border-color: var(--primary); color: var(--primary); }

/* ── Outline Tab ─────────────────────────────────────────── */
.outline-section {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  margin-bottom: 0.8rem;
  overflow: hidden;
  box-shadow: var(--shadow);
}
.outline-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0.9rem 1.2rem;
  cursor: pointer;
  user-select: none;
  transition: background var(--transition);
}
.outline-head:hover { background: var(--primary-light); }
.outline-head h3 { font-size: 0.98rem; font-weight: 600; color: var(--primary); }
.outline-head .outline-toggle { font-size: 0.8rem; color: var(--text-muted); transition: transform var(--transition); }
.outline-head.open .outline-toggle { transform: rotate(90deg); }
.outline-body { display: none; padding: 0 1.2rem 1rem; border-top: 1px solid var(--border); }
.outline-body.open { display: block; }
.outline-lecture { margin-top: 0.9rem; }
.outline-lecture-title {
  font-size: 0.85rem;
  font-weight: 600;
  color: var(--text);
  margin-bottom: 0.4rem;
  display: flex;
  align-items: center;
  gap: 0.5rem;
}
.outline-lecture-title .lecture-badge {
  font-size: 0.68rem;
  font-weight: 700;
  background: var(--primary-light);
  color: var(--primary);
  padding: 0.1rem 0.45rem;
  border-radius: 4px;
}
.outline-points { list-style: none; padding: 0; }
.outline-points li {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 1rem;
  padding: 0.3rem 0.5rem;
  font-size: 0.85rem;
  border-radius: 4px;
  color: var(--text);
  transition: background var(--transition);
}
.outline-points li:hover { background: var(--surface-2); }
.outline-points .page-link {
  font-size: 0.75rem;
  color: var(--primary);
  white-space: nowrap;
  font-weight: 500;
  border: 1px solid var(--border);
  padding: 0.1rem 0.45rem;
  border-radius: 4px;
  text-decoration: none;
  flex-shrink: 0;
}
.outline-points .page-link:hover { background: var(--primary); color: #fff; border-color: var(--primary); }

/* ── Empty State ─────────────────────────────────────────── */
.empty-state { text-align: center; padding: 3rem 1rem; color: var(--text-muted); }
.empty-state h3 { font-size: 1rem; margin-bottom: 0.4rem; }
.empty-state p  { font-size: 0.85rem; }

/* ── Loading ─────────────────────────────────────────────── */
.loading { text-align: center; padding: 2rem; color: var(--text-muted); font-size: 0.9rem; }

/* ── Scrollbar ───────────────────────────────────────────── */
::-webkit-scrollbar { width: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-strong); border-radius: 4px; }

/* ── Responsive ──────────────────────────────────────────── */
@media (max-width: 700px) {
  .site-header  { padding: 0 1rem; }
  .course-layout{ padding: 1rem; }
  .q-card-head  { flex-wrap: wrap; gap: 0.4rem; }
}

/* ── Content area ────────────────────────────────────────── */
#content-area { display: block; }

/* ── Favorites star ─────────────────────────────────────── */
.q-star {
  background: none; border: none; cursor: pointer;
  font-size: 18px; color: #ccc; transition: color .18s; line-height: 1; padding: 0;
}
.q-star.starred { color: #f5a623; }

/* ── Mini pie (错题集) ───────────────────────────────────── */
.wrong-stat { display: flex; align-items: center; gap: 8px; }
.mini-pie-wrap { flex-shrink: 0; }

/* ── Bilingual explanation ───────────────────────────────── */
.explanation-en { color: var(--text); }
.explanation-zh {
  color: #555; font-size: .9em; margin-top: 6px;
  padding-top: 6px; border-top: 1px dashed #dde; line-height: 1.6;
}

/* ── Pagination nav ─────────────────────────────────────── */
#pagination-nav {
  display: flex; align-items: center;
  justify-content: center; gap: 12px; padding: 14px 0 6px;
}
#pagination-nav .btn-outline {
  padding: .38rem .9rem; border: 1px solid var(--border);
  background: var(--surface); border-radius: var(--radius-sm);
  font-size: .82rem; font-weight: 500; color: var(--text-muted);
  transition: all var(--transition);
}
#pagination-nav .btn-outline:hover:not(:disabled) { border-color: var(--primary); color: var(--primary); }
#pagination-nav .btn-outline:disabled { opacity: .38; cursor: not-allowed; }
#pagination-nav .btn-finish {
  padding: .38rem .9rem; background: var(--primary); color: #fff;
  border: none; border-radius: var(--radius-sm); font-size: .82rem; font-weight: 600;
  transition: background var(--transition);
}
#pagination-nav .btn-finish:hover { background: var(--primary-dark); }

/* ── Mindmap ────────────────────────────────────────────── */
#mindmap-controls { padding: 10px 0; display: flex; gap: 8px; flex-wrap: wrap; align-items: center; margin-bottom: 8px; }
#mindmap-svg-container {
  width: 100%; overflow: auto;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
}
.mm-link { fill: none; stroke: #ccc; stroke-width: 1.5px; }
.mm-node text { font: 12px 'Inter', sans-serif; fill: var(--text); }

/* ── Vocab cards (百词斩 style) ──────────────────────────── */
.vocab-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(200px, 1fr));
  gap: 10px;
  margin-top: 12px;
}
.vocab-card {
  border-radius: var(--radius);
  padding: 12px 14px;
  border: 1.5px solid;
  cursor: pointer;
  transition: transform 0.12s, box-shadow 0.12s;
  display: flex;
  flex-direction: column;
  gap: 4px;
}
.vocab-card:hover { transform: translateY(-2px); box-shadow: 0 4px 16px rgba(104,117,200,0.13); }
.vocab-card-term { font-size: 0.97rem; font-weight: 700; color: var(--text); line-height: 1.3; }
.vocab-card-zh   { font-size: 0.82rem; color: #555; line-height: 1.4; }
.vocab-card-go   { font-size: 0.73rem; margin-top: 4px; opacity: 0.6; }
.vocab-card-del  {
  position: absolute; top: 5px; right: 6px;
  background: none; border: none; cursor: pointer;
  font-size: 0.9rem; color: var(--text-muted); opacity: 0.4;
  line-height: 1; padding: 0;
}
.vocab-card-del:hover { opacity: 1; color: #c0392b; }
.vocab-card.vocab-correct { background: #EEF5F1; border-color: #5B8A6F; }
.vocab-card.vocab-wrong   { background: #F9EEEE; border-color: #B85C5C; }
.vocab-card.vocab-mixed   { background: #FFF8E6; border-color: #c9a44a; }
.vocab-card.vocab-neutral { background: #F5F6FB; border-color: #ddd; }
.vocab-card.vocab-neutral:hover { border-color: var(--primary); }
.vocab-section-label {
  font-size: 0.78rem;
  font-weight: 700;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
  padding: 6px 0 2px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 4px;
  display: flex;
  align-items: center;
  gap: 8px;
}
.vocab-section-count {
  font-weight: 400;
  font-size: 0.72rem;
  color: var(--text-muted);
  opacity: 0.7;
}
.vocab-add-form {
  background: var(--surface);
  border: 1.5px solid var(--border);
  border-radius: var(--radius);
  padding: 14px;
  margin-bottom: 12px;
  display: none;
}
.vocab-add-form.visible { display: block; }
.vocab-add-form input {
  width: 100%;
  padding: 7px 10px;
  border: 1.5px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 0.88rem;
  font-family: inherit;
  color: var(--text);
  background: var(--bg);
  margin-bottom: 7px;
  box-sizing: border-box;
  outline: none;
}
.vocab-add-form input:focus { border-color: var(--primary); }

/* ── Shared utils ───────────────────────────────────────── */
.tab-panel { box-sizing: border-box; }
.btn-small {
  padding: 4px 10px; font-size: .78em; border-radius: var(--radius-sm);
  background: var(--primary); color: #fff; border: none; cursor: pointer;
}
.btn-small:hover { background: var(--primary-dark); }
.btn-small.secondary { background: var(--text-muted); }
.btn-small.secondary:hover { background: #555; }