/* ---------- Theme tokens ---------- */
:root {
  --bg: #f8fafc;
  --surface: #ffffff;
  --surface-2: #f1f5f9;
  --border: #e2e8f0;
  --border-strong: #cbd5e1;
  --text: #0f172a;
  --text-2: #334155;
  --muted: #64748b;
  --primary: #2563eb;
  --primary-hover: #1d4ed8;
  --primary-soft: #eff6ff;
  --primary-border: #bfdbfe;
  --teal: #0d9488;
  --success: #16a34a;
  --success-soft: #f0fdf4;
  --success-border: #86efac;
  --danger: #dc2626;
  --danger-soft: #fef2f2;
  --danger-border: #fca5a5;
  --warn: #d97706;
  --code-bg: #f1f5f9;
  --shadow: 0 1px 2px rgba(15, 23, 42, .04), 0 1px 3px rgba(15, 23, 42, .06);
  --radius: 12px;
  --font: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, "Cascadia Code", Consolas, monospace;
  color-scheme: light;
}

:root[data-theme="dark"] {
  --bg: #0b1120;
  --surface: #111827;
  --surface-2: #1e293b;
  --border: #1f2a3c;
  --border-strong: #334155;
  --text: #e2e8f0;
  --text-2: #cbd5e1;
  --muted: #94a3b8;
  --primary: #3b82f6;
  --primary-hover: #60a5fa;
  --primary-soft: rgba(59, 130, 246, .14);
  --primary-border: rgba(96, 165, 250, .45);
  --teal: #14b8a6;
  --success: #22c55e;
  --success-soft: rgba(34, 197, 94, .12);
  --success-border: rgba(74, 222, 128, .5);
  --danger: #f87171;
  --danger-soft: rgba(248, 113, 113, .12);
  --danger-border: rgba(248, 113, 113, .5);
  --warn: #fbbf24;
  --code-bg: #1e293b;
  --shadow: 0 1px 2px rgba(0, 0, 0, .3);
  color-scheme: dark;
}

/* ---------- Base ---------- */
* { box-sizing: border-box; }
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 15px/1.6 var(--font);
  -webkit-font-smoothing: antialiased;
  transition: background-color .2s, color .2s;
}

button, input { font: inherit; color: inherit; }
.muted { color: var(--muted); }
.small { font-size: 12.5px; }
.mono { font-family: var(--mono); }
.mono-label { font-family: var(--mono); font-size: 12.5px; font-weight: 600; letter-spacing: .06em; }

code {
  font-family: var(--mono);
  font-size: .9em;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: 5px;
  padding: .05em .35em;
}

kbd {
  font-family: var(--mono);
  font-size: 11px;
  border: 1px solid currentColor;
  border-radius: 4px;
  padding: 0 5px;
  opacity: .8;
}

/* ---------- Top bar ---------- */
.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 16px;
  padding: 10px clamp(16px, 3vw, 40px);
  background: color-mix(in srgb, var(--surface) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--border);
}

.brand { display: flex; align-items: center; gap: 10px; }
.brand-logo {
  display: grid; place-items: center;
  width: 36px; height: 36px;
  border-radius: 10px;
  background: var(--primary);
  color: #fff;
}
.brand-name { font-weight: 700; font-size: 17px; line-height: 1.2; }
.brand-sub { font-size: 12px; color: var(--muted); }

.icon-btn {
  display: grid; place-items: center;
  width: 38px; height: 38px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  cursor: pointer;
  transition: background-color .15s, border-color .15s;
}
.icon-btn:hover { background: var(--surface-2); border-color: var(--border-strong); }
.icon-sun { display: none; }
[data-theme="dark"] .icon-sun { display: block; }
[data-theme="dark"] .icon-moon { display: none; }

/* ---------- Page ---------- */
.page {
  max-width: 1560px;
  margin: 0 auto;
  padding: 14px clamp(16px, 3vw, 40px) 32px;
}

.toolbar { display: flex; gap: 10px; align-items: stretch; }

.tabs {
  flex: 1;
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 4px;
  padding: 4px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}

.tab {
  display: flex; align-items: center; justify-content: center; gap: 8px;
  padding: 9px 12px;
  border: 0;
  border-radius: 9px;
  background: transparent;
  color: var(--text-2);
  font-size: 13.5px;
  cursor: pointer;
  transition: background-color .15s, color .15s;
}
.tab:hover { background: var(--surface-2); }
.tab.active { background: var(--primary); color: #fff; font-weight: 600; }
.tab .count {
  font-family: var(--mono);
  font-size: 11px;
  padding: 0 7px;
  border-radius: 99px;
  background: var(--surface-2);
  color: var(--muted);
}
.tab.active .count { background: rgba(255, 255, 255, .22); color: #fff; }

/* ---------- Buttons ---------- */
.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 8px;
  padding: 9px 16px;
  border-radius: 10px;
  border: 1px solid transparent;
  font-weight: 500;
  cursor: pointer;
  white-space: nowrap;
  transition: background-color .15s, border-color .15s, color .15s, opacity .15s;
}
.btn:disabled { opacity: .45; cursor: not-allowed; }
.btn-primary { background: var(--primary); color: #fff; font-weight: 600; }
.btn-primary:hover:not(:disabled) { background: var(--primary-hover); }
.btn-outline { background: var(--surface); border-color: var(--border); color: var(--text-2); }
.btn-outline:hover:not(:disabled) { background: var(--surface-2); border-color: var(--border-strong); }
.btn-sm { padding: 5px 11px; font-size: 13px; border-radius: 8px; }
.btn-danger { background: var(--danger); color: #fff; border-color: var(--danger); }
.btn.flagged { color: var(--warn); border-color: var(--warn); }
.btn.flagged svg { fill: currentColor; }

/* ---------- Progress ---------- */
.progress { margin: 18px 0 20px; }
.progress-text { display: flex; justify-content: space-between; gap: 12px; font-weight: 500; font-size: 14px; margin-bottom: 6px; }
.score { color: var(--muted); font-weight: 400; }
.progress-track { height: 6px; border-radius: 99px; background: var(--surface-2); overflow: hidden; }
.progress-bar { height: 100%; width: 0; background: var(--teal); border-radius: 99px; transition: width .3s; }

/* ---------- Layout ---------- */
.layout { display: grid; grid-template-columns: 216px minmax(0, 1fr); gap: 20px; align-items: start; }

.sidebar {
  position: sticky;
  top: 76px;
  max-height: calc(100vh - 96px);
  display: flex; flex-direction: column;
  padding: 14px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
}
.sidebar-head { padding-bottom: 10px; margin-bottom: 12px; border-bottom: 1px solid var(--border); line-height: 1.4; }

.goto { display: flex; gap: 6px; margin-bottom: 12px; }
.goto input {
  flex: 1; min-width: 0;
  padding: 8px 12px;
  border: 1px solid var(--border);
  border-radius: 9px;
  background: var(--surface);
  outline: none;
}
.goto input:focus { border-color: var(--primary); box-shadow: 0 0 0 3px var(--primary-soft); }
.goto input::-webkit-inner-spin-button { display: none; }
.goto .btn { padding: 8px 12px; }

.map {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  overflow-y: auto;
  padding: 3px;
  margin: -3px;
  scrollbar-width: thin;
}
.cell {
  position: relative;
  aspect-ratio: 1;
  display: grid; place-items: center;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: var(--surface);
  font-family: var(--mono);
  font-size: 12px;
  color: var(--text-2);
  cursor: pointer;
  transition: background-color .15s, border-color .15s;
}
.cell:hover { border-color: var(--border-strong); background: var(--surface-2); }
.cell.picked { background: var(--primary-soft); border-color: var(--primary-border); }
.cell.correct { background: var(--success-soft); border-color: var(--success-border); color: var(--success); font-weight: 600; }
.cell.wrong { background: var(--danger-soft); border-color: var(--danger-border); color: var(--danger); font-weight: 600; }
.cell.current { border: 2px solid var(--primary); box-shadow: 0 0 0 2px var(--primary-soft); }
.cell.flag::after {
  content: "";
  position: absolute; top: 3px; right: 3px;
  width: 6px; height: 6px; border-radius: 50%;
  background: var(--warn);
}

.legend { display: flex; flex-wrap: wrap; gap: 4px 12px; margin-top: 12px; padding-top: 10px; border-top: 1px solid var(--border); font-size: 11.5px; color: var(--muted); }
.legend span { display: inline-flex; align-items: center; gap: 5px; }
.dot { width: 9px; height: 9px; border-radius: 3px; display: inline-block; }
.dot-correct { background: var(--success); }
.dot-wrong { background: var(--danger); }
.dot-flag { background: var(--warn); border-radius: 50%; }

/* ---------- Question card ---------- */
.card {
  display: flex; flex-direction: column;
  min-height: 560px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 16px;
  box-shadow: var(--shadow);
}
.card-body { flex: 1; padding: 28px 28px 8px; }

.q-head { display: flex; justify-content: space-between; align-items: center; gap: 12px; margin-bottom: 20px; }
.q-title { display: flex; align-items: center; gap: 12px; font-weight: 600; }
.q-badge {
  display: grid; place-items: center;
  min-width: 32px; height: 32px; padding: 0 6px;
  border-radius: 8px;
  background: var(--primary-soft);
  border: 1px solid var(--primary-border);
  color: var(--primary);
  font-family: var(--mono);
  font-size: 14px;
}

.q-text { font-size: 17px; line-height: 1.7; max-width: 80ch; white-space: pre-line; }
.q-images { display: flex; flex-wrap: wrap; gap: 12px; margin-top: 16px; }
.q-images a { display: block; max-width: 100%; }
.q-images img {
  display: block;
  max-width: 100%;
  height: auto;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: #fff; /* images are drawn on white */
  padding: 6px;
}
.q-hint { margin: 22px 0 10px; font-size: 14px; }

.options { display: flex; flex-direction: column; gap: 10px; }
.option {
  display: flex; align-items: center; gap: 16px;
  width: 100%;
  padding: 16px 16px;
  text-align: left;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
  font-size: 14.5px;
  line-height: 1.55;
  cursor: pointer;
  transition: background-color .15s, border-color .15s;
}
.option:hover:not(:disabled):not(.selected) { border-color: var(--border-strong); background: var(--surface-2); }
.option:disabled { cursor: default; }
.option .letter {
  flex: none;
  display: grid; place-items: center;
  width: 28px; height: 28px;
  border-radius: 7px;
  background: var(--surface-2);
  font-family: var(--mono);
  font-size: 13px;
  font-weight: 600;
  color: var(--text-2);
}
.option .mark { margin-left: auto; flex: none; font-weight: 700; }
.option.selected { border-color: var(--primary); background: var(--primary-soft); }
.option.selected .letter { background: var(--primary); color: #fff; }
.option.correct { border-color: var(--success); background: var(--success-soft); }
.option.correct .letter { background: var(--success); color: #fff; }
.option.correct .mark { color: var(--success); }
.option.wrong { border-color: var(--danger); background: var(--danger-soft); }
.option.wrong .letter { background: var(--danger); color: #fff; }
.option.wrong .mark { color: var(--danger); }

.actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 22px; }
.actions .btn-primary { padding: 11px 20px; }
.actions .btn-primary kbd { border-color: rgba(255, 255, 255, .6); }

.result {
  margin-top: 20px;
  padding: 14px 16px;
  border-radius: 10px;
  border: 1px solid;
  font-size: 14.5px;
}
.result.ok { background: var(--success-soft); border-color: var(--success-border); }
.result.bad { background: var(--danger-soft); border-color: var(--danger-border); }
.result strong.ok { color: var(--success); }
.result strong.bad { color: var(--danger); }
.result .answer-line { margin-top: 4px; color: var(--text-2); }

.discussion {
  margin: 16px 0 12px;
  border: 1px solid var(--border);
  border-radius: 10px;
  background: var(--surface);
}
.discussion summary {
  padding: 12px 16px;
  font-weight: 600;
  cursor: pointer;
  list-style: none;
  display: flex; align-items: center; gap: 8px;
}
.discussion summary::before { content: "▸"; color: var(--muted); transition: transform .15s; }
.discussion[open] summary::before { transform: rotate(90deg); }
.discussion summary::-webkit-details-marker { display: none; }
.discussion ul { list-style: none; margin: 0; padding: 0 16px 8px; }
.discussion li { padding: 12px 0; border-top: 1px solid var(--border); font-size: 14px; color: var(--text-2); overflow-wrap: anywhere; }
.comment-meta { display: flex; align-items: center; gap: 8px; margin-bottom: 4px; font-size: 12.5px; color: var(--muted); }
.pill {
  font-family: var(--mono);
  font-size: 11.5px;
  font-weight: 600;
  padding: 1px 8px;
  border-radius: 99px;
  background: var(--primary-soft);
  color: var(--primary);
}
.pill.ok { background: var(--success-soft); color: var(--success); }

.card-foot {
  display: flex; align-items: center; justify-content: space-between; gap: 12px;
  padding: 10px;
  border-top: 1px solid var(--border);
  position: sticky;
  bottom: 0;
  background: var(--surface);
  border-radius: 0 0 16px 16px;
}
.pos { font-size: 13px; color: var(--text-2); }

.empty { flex: 1; display: grid; place-content: center; justify-items: center; gap: 8px; padding: 40px 20px; text-align: center; color: var(--muted); }

.shortcuts { text-align: center; margin-top: 18px; }
.shortcuts kbd { opacity: .7; }

/* ---------- Responsive ---------- */
@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; }
  .sidebar { position: static; max-height: none; }
  .map { grid-template-columns: repeat(auto-fill, minmax(42px, 1fr)); max-height: 180px; }
  .card { min-height: 0; }
}

@media (max-width: 600px) {
  .brand-sub { display: none; }
  .toolbar { flex-direction: column; }
  .tab { flex-direction: column; gap: 2px; padding: 7px 4px; font-size: 12px; }
  .tab svg { display: none; }
  .card-body { padding: 20px 16px 8px; }
  .q-text { font-size: 16px; }
  .option { padding: 13px 12px; gap: 12px; }
  .actions .btn kbd, .shortcuts { display: none; }
}