:root {
  --bg: #f5f6fa;
  --surface: #ffffff;
  --surface-2: #f0f1f6;
  --text: #1a1d29;
  --text-dim: #5a5f73;
  --border: #e2e4ee;
  --accent: #4f5bd5;
  --accent-2: #7c3aed;
  --good: #16a34a;
  --good-bg: #dcfce7;
  --warn: #d97706;
  --warn-bg: #fef3c7;
  --bad: #dc2626;
  --bad-bg: #fee2e2;
  --shadow: 0 1px 3px rgba(20,20,40,0.08), 0 1px 2px rgba(20,20,40,0.06);
  --radius: 14px;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #14151f;
    --surface: #1c1e2b;
    --surface-2: #23253470;
    --text: #eef0f8;
    --text-dim: #9a9fb5;
    --border: #2c2f42;
    --accent: #818cf8;
    --accent-2: #c084fc;
    --good: #4ade80;
    --good-bg: #14371f;
    --warn: #fbbf24;
    --warn-bg: #3a2b06;
    --bad: #f87171;
    --bad-bg: #3a1414;
    --shadow: 0 1px 3px rgba(0,0,0,0.4), 0 1px 2px rgba(0,0,0,0.3);
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Inter, Roboto, Helvetica, Arial, sans-serif;
  -webkit-font-smoothing: antialiased;
}

.topbar {
  position: sticky;
  top: 0;
  z-index: 20;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
  padding: 14px 20px 0;
}

.brand {
  display: flex;
  align-items: baseline;
  gap: 10px;
  flex-wrap: wrap;
  margin-bottom: 12px;
}
.brand-mark {
  font-weight: 800;
  font-size: 20px;
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  -webkit-background-clip: text;
  background-clip: text;
  color: transparent;
}
.brand-sub { color: var(--text-dim); font-size: 13px; }

.tabs {
  display: flex;
  gap: 4px;
  overflow-x: auto;
  scrollbar-width: none;
}
.tabs::-webkit-scrollbar { display: none; }

.tab-btn {
  appearance: none;
  border: none;
  background: transparent;
  color: var(--text-dim);
  font-size: 14px;
  font-weight: 600;
  padding: 10px 14px;
  border-radius: 10px 10px 0 0;
  cursor: pointer;
  white-space: nowrap;
  border-bottom: 2px solid transparent;
}
.tab-btn:hover { color: var(--text); background: var(--surface-2); }
.tab-btn.active {
  color: var(--accent);
  border-bottom: 2px solid var(--accent);
}

#app {
  max-width: 920px;
  margin: 0 auto;
  padding: 20px 16px 60px;
}

.footer {
  text-align: center;
  color: var(--text-dim);
  font-size: 12px;
  padding: 20px;
}

/* Generic components */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: 18px;
  margin-bottom: 16px;
}

.section-title {
  font-size: 18px;
  font-weight: 700;
  margin: 0 0 4px;
}
.section-desc {
  color: var(--text-dim);
  font-size: 13px;
  margin: 0 0 16px;
}

.btn {
  appearance: none;
  border: 1px solid var(--border);
  background: var(--surface-2);
  color: var(--text);
  font-weight: 600;
  font-size: 14px;
  padding: 10px 16px;
  border-radius: 10px;
  cursor: pointer;
  transition: transform 0.05s ease;
}
.btn:hover { filter: brightness(1.05); }
.btn:active { transform: scale(0.98); }
.btn-primary {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  color: white;
  border: none;
}
.btn-row { display: flex; gap: 10px; flex-wrap: wrap; align-items: center; }
.btn:disabled { opacity: 0.5; cursor: not-allowed; }

select, input[type="text"], input[type="number"] {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  padding: 9px 12px;
  border-radius: 10px;
  font-size: 14px;
}

.pill {
  display: inline-block;
  font-size: 12px;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: 999px;
  background: var(--surface-2);
  color: var(--text-dim);
}

/* Dashboard */
.stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(140px, 1fr));
  gap: 12px;
  margin-bottom: 18px;
}
.stat-box {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 16px;
  box-shadow: var(--shadow);
}
.stat-num { font-size: 26px; font-weight: 800; }
.stat-label { color: var(--text-dim); font-size: 12px; margin-top: 2px; }

.mastery-row {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 10px 0;
  border-bottom: 1px solid var(--border);
}
.mastery-row:last-child { border-bottom: none; }
.mastery-name { flex: 1; font-weight: 600; font-size: 14px; }
.mastery-bar-track {
  flex: 2;
  height: 10px;
  background: var(--surface-2);
  border-radius: 999px;
  overflow: hidden;
}
.mastery-bar-fill { height: 100%; border-radius: 999px; transition: width 0.3s ease; }
.mastery-pct { width: 46px; text-align: right; font-size: 13px; font-weight: 700; color: var(--text-dim); }

/* Summaries */
.topic-block { margin-bottom: 14px; }
.topic-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  cursor: pointer;
  padding: 14px 18px;
}
.topic-header h3 { margin: 0; font-size: 16px; }
.topic-header .chev { color: var(--text-dim); transition: transform 0.2s ease; }
.topic-block.open .chev { transform: rotate(90deg); }
.topic-body {
  display: none;
  padding: 0 18px 16px;
}
.topic-block.open .topic-body { display: block; }
.topic-body ul { margin: 0; padding-left: 20px; }
.topic-body li { margin-bottom: 9px; line-height: 1.5; font-size: 14.5px; }

.search-row { margin-bottom: 16px; }
.search-row input { width: 100%; }

mark { background: #fde047; color: #1a1d29; border-radius: 3px; padding: 0 2px; }

/* Flashcards */
.fc-controls { display: flex; justify-content: space-between; align-items: center; flex-wrap: wrap; gap: 10px; margin-bottom: 16px; }
.fc-progress { color: var(--text-dim); font-size: 13px; }

.flashcard-stage {
  perspective: 1200px;
  max-width: 640px;
  margin: 0 auto 18px;
}
.flashcard {
  position: relative;
  min-height: 220px;
  transform-style: preserve-3d;
  transition: transform 0.5s cubic-bezier(.4,.2,.2,1);
  cursor: pointer;
}
.flashcard.flipped { transform: rotateY(180deg); }
.fc-face {
  position: absolute;
  inset: 0;
  backface-visibility: hidden;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  display: flex;
  align-items: center;
  justify-content: center;
  text-align: center;
  padding: 28px;
  font-size: 17px;
  line-height: 1.5;
}
.fc-face.back { transform: rotateY(180deg); background: var(--surface-2); }
.fc-tag { position: absolute; top: 12px; left: 16px; font-size: 11px; color: var(--text-dim); font-weight: 700; text-transform: uppercase; letter-spacing: 0.04em; }
.fc-hint { position: absolute; bottom: 12px; color: var(--text-dim); font-size: 12px; }

.fc-actions { display: flex; justify-content: center; gap: 12px; flex-wrap: wrap; }

/* Quiz & CBT */
.quiz-setup { display: flex; flex-direction: column; gap: 14px; }
.field-row { display: flex; flex-direction: column; gap: 6px; }
.field-row label { font-size: 13px; font-weight: 600; color: var(--text-dim); }

.q-progress { display: flex; justify-content: space-between; align-items: center; margin-bottom: 12px; font-size: 13px; color: var(--text-dim); }
.q-timer { font-weight: 800; color: var(--accent); font-variant-numeric: tabular-nums; }
.q-timer.low { color: var(--bad); }

.q-bar-track { height: 6px; background: var(--surface-2); border-radius: 999px; overflow: hidden; margin-bottom: 18px; }
.q-bar-fill { height: 100%; background: linear-gradient(135deg, var(--accent), var(--accent-2)); }

.q-question { font-size: 17px; font-weight: 600; margin-bottom: 18px; line-height: 1.5; }
.q-options { display: flex; flex-direction: column; gap: 10px; }
.q-option {
  text-align: left;
  padding: 13px 16px;
  border-radius: 12px;
  border: 1px solid var(--border);
  background: var(--surface);
  cursor: pointer;
  font-size: 14.5px;
  display: flex;
  gap: 10px;
}
.q-option:hover { border-color: var(--accent); }
.q-option .opt-letter { font-weight: 700; color: var(--text-dim); }
.q-option.selected { border-color: var(--accent); background: var(--surface-2); }
.q-option.correct { border-color: var(--good); background: var(--good-bg); }
.q-option.incorrect { border-color: var(--bad); background: var(--bad-bg); }
.q-option:disabled, .q-option.locked { cursor: default; }

.q-explain { margin-top: 14px; padding: 12px 14px; border-radius: 10px; background: var(--surface-2); font-size: 13.5px; color: var(--text-dim); }
.q-explain.show-correct { color: var(--good); }
.q-explain.show-incorrect { color: var(--bad); }

.q-nav { display: flex; justify-content: space-between; margin-top: 20px; }

.result-score { font-size: 42px; font-weight: 800; text-align: center; margin: 6px 0; }
.result-sub { text-align: center; color: var(--text-dim); margin-bottom: 24px; }

.review-item { border-bottom: 1px solid var(--border); padding: 14px 0; }
.review-item:last-child { border-bottom: none; }
.review-q { font-weight: 600; margin-bottom: 8px; }
.review-answer { font-size: 13.5px; margin-bottom: 4px; }
.review-answer.ok { color: var(--good); }
.review-answer.bad { color: var(--bad); }

@media (max-width: 560px) {
  .stat-grid { grid-template-columns: repeat(2, 1fr); }
  .flashcard-stage { min-height: 200px; }
}