:root {
  --bg: #f2f5fa;
  --card-bg: #ffffff;
  --text: #1c2430;
  --text-muted: #5c6779;
  --border: #d8e0ee;
  --primary: #3e6fbf;
  --primary-hover: #325aa0;
  --danger: #d84343;
  --danger-hover: #c13636;
  --success: #3f9d5d;
  --success-bg: #e3f5e9;
  --error-bg: #fdeceb;
  --chip-bg: #e7edf8;
  --chip-bg-active: #cbdaf3;
  --shadow: 0 1px 3px rgba(0,0,0,0.06), 0 1px 2px rgba(0,0,0,0.04);
}

:root[data-theme="dark"] {
  --bg: #12151f;
  --card-bg: #1b2030;
  --text: #e7ebf5;
  --text-muted: #9aa5bc;
  --border: #2c3550;
  --primary: #7fa6f0;
  --primary-hover: #96b8f4;
  --danger: #e5645f;
  --danger-hover: #ea7d78;
  --success: #4cc27c;
  --success-bg: #1c3427;
  --error-bg: #3a1e22;
  --chip-bg: #232b42;
  --chip-bg-active: #35406a;
  --shadow: 0 1px 3px rgba(0,0,0,0.3), 0 1px 2px rgba(0,0,0,0.2);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #12151f;
    --card-bg: #1b2030;
    --text: #e7ebf5;
    --text-muted: #9aa5bc;
    --border: #2c3550;
    --primary: #7fa6f0;
    --primary-hover: #96b8f4;
    --danger: #e5645f;
    --danger-hover: #ea7d78;
    --success: #4cc27c;
    --success-bg: #1c3427;
    --error-bg: #3a1e22;
    --chip-bg: #232b42;
    --chip-bg-active: #35406a;
    --shadow: 0 1px 3px rgba(0,0,0,0.3), 0 1px 2px rgba(0,0,0,0.2);
  }
}

@font-face {
  font-family: "Inter Variable";
  font-style: normal;
  font-weight: 100 900;
  font-display: swap;
  src: url("fonts/InterVariable.woff2") format("woff2");
}

* { box-sizing: border-box; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: "Inter Variable", -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  font-optical-sizing: auto;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-size: 16px;
  line-height: 1.65;
}

#app {
  max-width: 1200px;
  margin: 0 auto;
  padding: 24px 16px 60px;
}

@media (min-width: 601px) {
  /* clears the fixed theme-toggle button so it never overlaps the
     quiz screen's Exit button or other top-of-card content */
  #app { padding-top: 56px; }
}

.hidden { display: none !important; }

.theme-toggle-btn {
  position: fixed;
  top: calc(14px + env(safe-area-inset-top));
  right: calc(14px + env(safe-area-inset-right));
  z-index: 10;
  background: var(--chip-bg);
  color: var(--text);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 7px 14px;
  font-size: 0.8rem;
  font-weight: 600;
  cursor: pointer;
}
.theme-toggle-btn:hover { background: var(--chip-bg-active); }

@media (max-width: 600px) {
  .theme-toggle-btn {
    position: static;
    display: block;
    width: fit-content;
    margin: 0 0 14px auto;
  }
}

.app-header {
  text-align: center;
  margin-bottom: 24px;
}
.app-header h1 {
  margin: 0 0 4px;
  font-size: 1.6rem;
}
.subtitle {
  color: var(--text-muted);
  margin: 0;
  font-size: 0.95rem;
}

.card {
  background: var(--card-bg);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 18px 20px;
  margin-bottom: 16px;
  box-shadow: var(--shadow);
}
.card h2 {
  font-size: 1rem;
  margin: 0 0 12px;
  color: var(--text-muted);
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.02em;
}
.card h3 {
  margin: 0 0 12px;
  font-size: 1.05rem;
}

.option-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 10px;
  margin-bottom: 14px;
}
.option-grid:last-child { margin-bottom: 0; }

.source-tier-label {
  font-size: 0.78rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  margin: 4px 0 8px;
}
.source-tier-label:first-child { margin-top: 0; }

.pill-radio {
  display: flex;
  align-items: center;
  gap: 8px;
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 10px 12px;
  cursor: pointer;
  font-size: 0.92rem;
  transition: border-color 0.15s, background 0.15s;
}
.pill-radio:has(input:checked) {
  border-color: var(--primary);
}
.pill-radio small {
  display: block;
  color: var(--text-muted);
  font-weight: 400;
  font-size: 0.78rem;
}
.pill-radio input { accent-color: var(--primary); }

.chip {
  display: flex;
  align-items: center;
  gap: 6px;
  background: var(--chip-bg);
  border-radius: 20px;
  padding: 7px 12px;
  font-size: 0.85rem;
  cursor: pointer;
}
.chip:has(input:checked) {
  background: var(--chip-bg-active);
}
.chip input { accent-color: var(--primary); }

#ka-select {
  display: flex;
  flex-direction: column;
  gap: 2px;
}
.ka-row {
  display: flex;
  align-items: center;
  gap: 10px;
  padding: 9px 4px;
  font-size: 0.92rem;
  cursor: pointer;
  border-bottom: 1px solid var(--border);
}
.ka-row:last-child { border-bottom: none; }
.ka-row input { accent-color: var(--primary); flex-shrink: 0; }

.ka-actions {
  margin-bottom: 12px;
  display: flex;
  gap: 16px;
}
.link-btn {
  background: none;
  border: none;
  color: var(--primary);
  cursor: pointer;
  font-size: 0.82rem;
  padding: 0;
}
.link-btn:hover { text-decoration: underline; }

.row-between {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  flex-wrap: wrap;
}

.btn {
  border: none;
  border-radius: 8px;
  padding: 11px 18px;
  font-size: 0.95rem;
  font-weight: 600;
  cursor: pointer;
  transition: background 0.15s, opacity 0.15s;
}
.btn:disabled { opacity: 0.45; cursor: not-allowed; }
.btn-primary { background: var(--primary); color: #fff; }
.btn-primary:hover:not(:disabled) { background: var(--primary-hover); }
.btn-secondary { background: var(--chip-bg); color: var(--text); }
.btn-secondary:hover:not(:disabled) { background: var(--chip-bg-active); }
.btn-danger { background: var(--danger); color: #fff; }
.btn-danger:hover:not(:disabled) { background: var(--danger-hover); }
.btn-ghost { background: none; border: 1px solid var(--border); color: var(--text-muted); }

/* Quiz screen */
.quiz-topbar {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 16px;
}
.quiz-progress { flex: 1; }
.quiz-progress span {
  font-size: 0.82rem;
  color: var(--text-muted);
}
.progress-bar {
  background: var(--border);
  border-radius: 6px;
  height: 6px;
  margin-top: 6px;
  overflow: hidden;
}
.progress-fill {
  background: var(--primary);
  height: 100%;
  width: 0%;
  transition: width 0.2s;
}
.quiz-timer {
  font-variant-numeric: tabular-nums;
  font-weight: 700;
  padding: 6px 12px;
  background: var(--chip-bg);
  border-radius: 8px;
  font-size: 0.9rem;
}
.quiz-timer.low-time { color: var(--danger); background: var(--error-bg); }

.question-card { min-height: 320px; }
.question-meta {
  display: flex;
  justify-content: space-between;
  align-items: center;
  margin-bottom: 10px;
}
.ka-tag {
  display: inline-block;
  background: var(--chip-bg-active);
  color: var(--primary);
  font-size: 0.75rem;
  font-weight: 700;
  padding: 3px 10px;
  border-radius: 20px;
}
.bookmark-btn {
  background: none;
  border: none;
  font-size: 1.4rem;
  cursor: pointer;
  color: var(--text-muted);
  line-height: 1;
  padding: 2px 4px;
}
.bookmark-btn.active { color: #e8b923; }

.question-text {
  font-size: 1.1rem;
  line-height: 1.6;
  margin: 0 0 18px;
}

.options-list {
  display: flex;
  flex-direction: column;
  gap: 10px;
}
.option-btn {
  display: flex;
  gap: 10px;
  text-align: left;
  border: 1px solid var(--border);
  background: var(--card-bg);
  color: var(--text);
  border-radius: 10px;
  padding: 12px 14px;
  cursor: pointer;
  font-size: 1rem;
  line-height: 1.55;
  transition: border-color 0.15s, background 0.15s;
}
.option-btn:hover:not(:disabled) { border-color: var(--primary); }
.option-btn .opt-letter { font-weight: 700; flex-shrink: 0; }
.option-btn.selected { border-color: var(--primary); background: var(--chip-bg-active); }
.option-btn.correct { border-color: var(--success); background: var(--success-bg); }
.option-btn.incorrect { border-color: var(--danger); background: var(--error-bg); }
.option-btn:disabled { cursor: default; }

.explanation-box {
  margin-top: 16px;
  padding: 14px 16px;
  background: var(--chip-bg);
  border-radius: 10px;
  font-size: 0.96rem;
  line-height: 1.6;
  border-left: 3px solid var(--primary);
}
.explanation-box .expl-label {
  font-weight: 700;
  margin-bottom: 6px;
  display: block;
}
.explanation-box p,
.rq-expl p {
  margin: 0 0 10px;
}
.explanation-box p:last-child,
.rq-expl p:last-child {
  margin-bottom: 0;
}

.quiz-nav {
  display: flex;
  gap: 10px;
  justify-content: space-between;
}
.quiz-nav .btn { flex: 1; }

/* Result screen */
.result-summary { text-align: center; }
.score-big { font-size: 2.4rem; font-weight: 800; }
.score-pct { color: var(--text-muted); font-size: 1.1rem; }

.ka-table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9rem;
}
.ka-table th, .ka-table td {
  text-align: left;
  padding: 8px 6px;
  border-bottom: 1px solid var(--border);
}
.ka-table th { color: var(--text-muted); font-weight: 600; font-size: 0.8rem; }

.review-item {
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 14px 16px;
  margin-bottom: 12px;
}
.review-item.wrong { border-left: 4px solid var(--danger); }
.review-item.correct { border-left: 4px solid var(--success); }
.review-item .rq-head {
  display: flex;
  justify-content: space-between;
  gap: 8px;
  margin-bottom: 8px;
  font-size: 0.8rem;
  color: var(--text-muted);
}
.review-item .rq-text { margin: 0 0 10px; font-weight: 600; font-size: 1rem; line-height: 1.55; }
.review-item .rq-answer { font-size: 0.94rem; margin: 2px 0; line-height: 1.55; }
.review-item .rq-answer.wrong-ans { color: var(--danger); }
.review-item .rq-answer.correct-ans { color: var(--success); }
.review-item .rq-expl {
  margin-top: 8px;
  font-size: 0.94rem;
  line-height: 1.6;
  color: var(--text-muted);
}

@media (max-width: 480px) {
  .quiz-nav { flex-wrap: wrap; }
  .quiz-topbar { flex-wrap: wrap; }
}