:root {
  --bg: #f6f7f9;
  --surface: #ffffff;
  --surface-2: #f0f2f5;
  --text: #16191d;
  --muted: #5f6672;
  --line: #dfe3e8;
  --accent: #1f6feb;
  --accent-soft: #e7f0fe;
  --good: #1a7f47;
  --good-soft: #e4f5ea;
  --bad: #c0362c;
  --bad-soft: #fdeceb;
  --warn: #9a6700;
  --radius: 12px;
  --shadow: 0 1px 2px rgba(16, 24, 40, .06), 0 1px 3px rgba(16, 24, 40, .1);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #0f1115;
    --surface: #171a20;
    --surface-2: #1e222a;
    --text: #e7e9ee;
    --muted: #9aa1ad;
    --line: #2b3039;
    --accent: #5b9dff;
    --accent-soft: #16233a;
    --good: #4ec27f;
    --good-soft: #12291d;
    --bad: #f2776a;
    --bad-soft: #2c1614;
    --warn: #d9a441;
    --shadow: 0 1px 2px rgba(0, 0, 0, .4);
  }
}

:root[data-theme="light"] {
  color-scheme: light;
  --bg: #f6f7f9; --surface: #fff; --surface-2: #f0f2f5;
  --text: #16191d; --muted: #5f6672; --line: #dfe3e8;
  --accent: #1f6feb; --accent-soft: #e7f0fe;
  --good: #1a7f47; --good-soft: #e4f5ea;
  --bad: #c0362c; --bad-soft: #fdeceb; --warn: #9a6700;
  --shadow: 0 1px 2px rgba(16,24,40,.06), 0 1px 3px rgba(16,24,40,.1);
}

:root[data-theme="dark"] {
  color-scheme: dark;
  --bg: #0f1115; --surface: #171a20; --surface-2: #1e222a;
  --text: #e7e9ee; --muted: #9aa1ad; --line: #2b3039;
  --accent: #5b9dff; --accent-soft: #16233a;
  --good: #4ec27f; --good-soft: #12291d;
  --bad: #f2776a; --bad-soft: #2c1614; --warn: #d9a441;
  --shadow: 0 1px 2px rgba(0,0,0,.4);
}

* { box-sizing: border-box; }

/* Author-level `display` declarations below would otherwise beat the UA
   stylesheet's [hidden] rule, so restate it with priority. */
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.55 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
        "Helvetica Neue", Arial, sans-serif;
  -webkit-text-size-adjust: 100%;
}

/* ── Top bar ─────────────────────────────────────────── */
.topbar {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
  padding: .75rem 1.25rem;
  background: color-mix(in srgb, var(--surface) 88%, transparent);
  backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line);
}

.brand {
  font-weight: 700;
  letter-spacing: -.01em;
  color: var(--text);
  text-decoration: none;
}
.brand span { color: var(--muted); font-weight: 500; }

.topbar-right { display: flex; align-items: center; gap: .6rem; }

.timer {
  font-variant-numeric: tabular-nums;
  font-weight: 600;
  padding: .25rem .6rem;
  border-radius: 999px;
  background: var(--surface-2);
  border: 1px solid var(--line);
}
.timer.low { color: var(--bad); border-color: var(--bad); }

.icon-btn {
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--text);
  border-radius: 8px;
  width: 2rem;
  height: 2rem;
  cursor: pointer;
  font-size: 1rem;
  line-height: 1;
}

/* ── Layout ──────────────────────────────────────────── */
main { max-width: 780px; margin: 0 auto; padding: 1.5rem 1.25rem 4rem; }
.view > * + * { margin-top: 1rem; }
h1 { font-size: 1.6rem; line-height: 1.25; margin: 0; letter-spacing: -.02em; }
h2 { font-size: 1.05rem; margin: 0 0 .75rem; letter-spacing: -.01em; }
.lede { color: var(--muted); margin: .25rem 0 0; }
.muted { color: var(--muted); }

.card {
  background: var(--surface);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 1.1rem;
  box-shadow: var(--shadow);
}

fieldset.card { margin: 0; }
legend { font-weight: 600; padding: 0 .4rem; }

/* ── Forms ───────────────────────────────────────────── */
.set-list { display: grid; gap: .5rem; margin-bottom: .85rem; }

.check, .set-option {
  display: flex;
  gap: .65rem;
  align-items: flex-start;
  padding: .55rem .1rem;
  cursor: pointer;
}
.check input, .set-option input { margin-top: .3rem; flex: none; accent-color: var(--accent); }
.check small, .set-option small { display: block; color: var(--muted); font-size: .85rem; }

.field { display: block; margin: .5rem 0 1rem; }
.field > span { display: block; font-weight: 500; margin-bottom: .3rem; }
.field input {
  width: 100%;
  padding: .5rem .65rem;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--surface-2);
  color: var(--text);
  font: inherit;
}
.field small { display: block; color: var(--muted); font-size: .85rem; margin-top: .3rem; }

.btn {
  font: inherit;
  font-weight: 500;
  padding: .55rem 1rem;
  border-radius: 9px;
  border: 1px solid var(--line);
  background: var(--surface);
  color: var(--text);
  cursor: pointer;
}
.btn:hover:not(:disabled) { background: var(--surface-2); }
.btn:disabled { opacity: .45; cursor: default; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.primary:hover:not(:disabled) { filter: brightness(1.08); }
.btn.quiet { border-color: transparent; background: transparent; color: var(--muted); }
.btn.small { padding: .3rem .65rem; font-size: .85rem; }
.btn.big { width: 100%; padding: .8rem; font-size: 1.02rem; }
.btn.active { background: var(--accent-soft); border-color: var(--accent); color: var(--accent); }

.error { color: var(--bad); font-weight: 500; }

.banner {
  display: flex;
  flex-wrap: wrap;
  gap: .75rem;
  align-items: center;
  justify-content: space-between;
  background: var(--accent-soft);
  border: 1px solid var(--accent);
  border-radius: var(--radius);
  padding: .85rem 1rem;
}
.banner span { display: block; color: var(--muted); font-size: .9rem; }
.banner-actions { display: flex; gap: .5rem; }

/* ── Exam ────────────────────────────────────────────── */
.exam-progress { display: flex; align-items: center; gap: .75rem; }
.exam-progress .bar {
  flex: 1;
  height: 6px;
  border-radius: 999px;
  background: var(--surface-2);
  border: 1px solid var(--line);
  overflow: hidden;
}
#progress-fill { height: 100%; width: 0; background: var(--accent); transition: width .2s; }
#progress-label { font-size: .85rem; color: var(--muted); font-variant-numeric: tabular-nums; }

.qmeta {
  display: flex;
  align-items: center;
  gap: .6rem;
  margin-bottom: .8rem;
  font-size: .85rem;
  color: var(--muted);
}
.qmeta #flag-btn { margin-left: auto; }
.qmeta #flag-btn.on { color: var(--warn); font-weight: 600; }

.tag {
  background: var(--surface-2);
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: .1rem .55rem;
  font-size: .78rem;
}

.stem { white-space: pre-wrap; }
.stem.rich { white-space: normal; }
.stem.rich p { margin: 0 0 .7rem; }
.stem.rich ul { margin: 0 0 .7rem; padding-left: 1.2rem; }
.stem table {
  border-collapse: collapse;
  margin: .2rem 0 .9rem;
  font-size: .9rem;
  min-width: 100%;
}
.stem table th, .stem table td {
  border: 1px solid var(--line);
  padding: .35rem .55rem;
  text-align: left;
  white-space: nowrap;
}
.stem table thead th, .stem table tbody th { background: var(--surface-2); font-weight: 600; }
.stem.rich { overflow-x: auto; }

.q-image {
  display: block;
  max-width: 100%;
  margin: .5rem 0 1rem;
  border-radius: 8px;
  background: #fff;
  padding: .5rem;
  border: 1px solid var(--line);
}

.instruction { font-weight: 600; margin: 1rem 0 .6rem; }

.options { display: grid; gap: .5rem; }

.option {
  display: flex;
  gap: .7rem;
  align-items: flex-start;
  padding: .7rem .85rem;
  border: 1px solid var(--line);
  border-radius: 10px;
  background: var(--surface-2);
  cursor: pointer;
}
.option:hover { border-color: var(--accent); }
.option input { margin-top: .28rem; flex: none; accent-color: var(--accent); }
.option.selected { border-color: var(--accent); background: var(--accent-soft); }
.option .label { font-weight: 600; margin-right: .1rem; }

.exam-nav { display: flex; gap: .5rem; flex-wrap: wrap; }
.exam-nav .primary { margin-left: auto; }

.navigator summary { cursor: pointer; font-weight: 600; }
.nav-grid {
  display: grid;
  grid-template-columns: repeat(auto-fill, minmax(2.4rem, 1fr));
  gap: .4rem;
  margin: .9rem 0;
}
.nav-grid button {
  font: inherit;
  font-size: .82rem;
  padding: .4rem 0;
  border-radius: 7px;
  border: 1px solid var(--line);
  background: var(--surface-2);
  color: var(--text);
  cursor: pointer;
}
.nav-grid button.answered { background: var(--accent-soft); border-color: var(--accent); color: var(--accent); }
.nav-grid button.flagged { border-color: var(--warn); }
.nav-grid button.current { outline: 2px solid var(--text); outline-offset: 1px; }

.legend { font-size: .82rem; color: var(--muted); display: flex; gap: 1rem; flex-wrap: wrap; margin: 0; }
.legend .dot { display: inline-block; width: .7rem; height: .7rem; border-radius: 3px; border: 1px solid var(--line); margin-right: .3rem; vertical-align: -1px; }
.legend .dot.answered { background: var(--accent-soft); border-color: var(--accent); }
.legend .dot.flagged { border-color: var(--warn); }
.legend .dot.current { outline: 2px solid var(--text); outline-offset: 1px; }

/* ── Results ─────────────────────────────────────────── */
.score-card { display: flex; gap: 1.5rem; align-items: center; flex-wrap: wrap; }

.ring {
  --pct: 0;
  --ring-color: var(--accent);
  flex: none;
  width: 122px;
  height: 122px;
  border-radius: 50%;
  display: grid;
  place-items: center;
  background:
    conic-gradient(var(--ring-color) calc(var(--pct) * 1%), var(--surface-2) 0);
}
.ring::before {
  content: "";
  grid-area: 1 / 1;
  width: 96px;
  height: 96px;
  border-radius: 50%;
  background: var(--surface);
}
.ring span {
  grid-area: 1 / 1;
  font-size: 1.6rem;
  font-weight: 700;
  font-variant-numeric: tabular-nums;
}
.ring.pass { --ring-color: var(--good); }
.ring.fail { --ring-color: var(--bad); }

.score-detail { flex: 1 1 16rem; }
.score-detail h1 { margin-bottom: .3rem; }
.score-actions { display: flex; gap: .5rem; flex-wrap: wrap; margin-top: .9rem; }

.chapters { display: grid; gap: .6rem; }
.chapter { display: grid; grid-template-columns: 1fr auto; gap: .2rem .75rem; font-size: .9rem; }
.chapter .cbar { grid-column: 1 / -1; height: 6px; border-radius: 999px; background: var(--surface-2); overflow: hidden; }
.chapter .cbar div { height: 100%; background: var(--accent); }
.chapter .cscore { font-variant-numeric: tabular-nums; color: var(--muted); }

.review-head { display: flex; align-items: center; justify-content: space-between; gap: 1rem; flex-wrap: wrap; }
.review-head h2 { margin: 0; }
.filters { display: flex; gap: .4rem; }

#review-list { display: grid; gap: .8rem; }

.review-item { border-left: 4px solid var(--line); }
.review-item.right { border-left-color: var(--good); }
.review-item.wrong { border-left-color: var(--bad); }

.verdict { font-weight: 700; font-size: .85rem; text-transform: uppercase; letter-spacing: .04em; }
.review-item.right .verdict { color: var(--good); }
.review-item.wrong .verdict { color: var(--bad); }

.review-options { display: grid; gap: .35rem; margin: .8rem 0; }
.review-option {
  display: flex;
  gap: .6rem;
  padding: .5rem .7rem;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: var(--surface-2);
  font-size: .95rem;
}
.review-option.correct { background: var(--good-soft); border-color: var(--good); }
.review-option.chosen-wrong { background: var(--bad-soft); border-color: var(--bad); }
.review-option .mark { flex: none; font-weight: 700; width: 1.1rem; }

.explanation {
  white-space: pre-wrap;
  background: var(--surface-2);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: .8rem;
  font-size: .92rem;
}
.explanation h3 { margin: 0 0 .4rem; font-size: .8rem; text-transform: uppercase; letter-spacing: .04em; color: var(--muted); }

/* ── Footer ──────────────────────────────────────────── */
.footer {
  max-width: 780px;
  margin: 0 auto;
  padding: 1.5rem 1.25rem 3rem;
  border-top: 1px solid var(--line);
  color: var(--muted);
  font-size: .82rem;
}
.footer p { margin: 0 0 .5rem; }

@media (max-width: 520px) {
  main { padding: 1rem .9rem 3rem; }
  .exam-nav .btn { flex: 1 1 auto; }
  .exam-nav .primary { margin-left: 0; flex-basis: 100%; }
}