:root {
  --bg: #0f1720;
  --panel: #17212b;
  --panel-2: #1e2a36;
  --line: #2c3b4a;
  --text: #e6edf3;
  --muted: #93a4b5;
  --accent: #3fa7d6;
  --accent-2: #2b7fa8;
  --ok: #3fb950;
  --ok-bg: #12301c;
  --bad: #f85149;
  --bad-bg: #3a1618;
  --warn: #d29922;
  --radius: 10px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font: 16px/1.6 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
}

a { color: var(--accent); }

header.site {
  background: linear-gradient(180deg, #1b2836, #131c26);
  border-bottom: 1px solid var(--line);
  padding: 18px 24px;
  position: sticky;
  top: 0;
  z-index: 20;
}

header.site .inner {
  max-width: 1100px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  gap: 20px;
  flex-wrap: wrap;
}

header.site h1 {
  font-size: 19px;
  margin: 0;
  letter-spacing: .2px;
}

header.site h1 span { color: var(--accent); }

nav.site { margin-left: auto; display: flex; gap: 8px; flex-wrap: wrap; }

nav.site a {
  color: var(--muted);
  text-decoration: none;
  padding: 7px 13px;
  border-radius: 7px;
  font-size: 14px;
  border: 1px solid transparent;
}

nav.site a:hover { color: var(--text); background: var(--panel-2); }

nav.site a.active {
  color: var(--text);
  background: var(--panel-2);
  border-color: var(--line);
}

main {
  max-width: 1100px;
  margin: 0 auto;
  padding: 28px 24px 80px;
}

h2 { font-size: 24px; margin: 34px 0 12px; }
h3 { font-size: 18px; margin: 26px 0 10px; color: var(--accent); }
h4 { font-size: 15px; margin: 20px 0 8px; }

p { margin: 10px 0; }

.card {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
  margin: 16px 0;
}

.note {
  background: #1a2733;
  border-left: 3px solid var(--accent);
  border-radius: 6px;
  padding: 12px 16px;
  margin: 16px 0;
  color: var(--muted);
  font-size: 14.5px;
}

.note strong { color: var(--text); }

table {
  width: 100%;
  border-collapse: collapse;
  margin: 14px 0;
  font-size: 14.5px;
}

th, td {
  border: 1px solid var(--line);
  padding: 8px 11px;
  text-align: left;
  vertical-align: top;
}

th { background: var(--panel-2); font-weight: 600; }

tbody tr:nth-child(even) { background: #141d26; }

code {
  background: #0b1219;
  border: 1px solid var(--line);
  border-radius: 4px;
  padding: 1px 5px;
  font-size: 13.5px;
}

pre {
  background: #0b1219;
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  overflow-x: auto;
}

pre code { border: 0; background: none; padding: 0; }

ul, ol { padding-left: 22px; }
li { margin: 5px 0; }

/* ---------- buttons ---------- */

button, .btn {
  font: inherit;
  font-size: 14.5px;
  cursor: pointer;
  border-radius: 8px;
  border: 1px solid var(--line);
  background: var(--panel-2);
  color: var(--text);
  padding: 10px 18px;
  transition: background .12s, border-color .12s;
}

button:hover:not(:disabled), .btn:hover { background: #26374a; border-color: #3d5266; }

button:disabled { opacity: .45; cursor: not-allowed; }

button.primary, .btn.primary {
  background: var(--accent-2);
  border-color: var(--accent);
  color: #fff;
  font-weight: 600;
}

button.primary:hover:not(:disabled) { background: var(--accent); }

button.ghost { background: transparent; }

/* ---------- exam setup ---------- */

.choice-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 14px;
  margin: 18px 0;
}

.choice {
  background: var(--panel);
  border: 2px solid var(--line);
  border-radius: var(--radius);
  padding: 18px;
  cursor: pointer;
  text-align: left;
  transition: border-color .12s, background .12s;
}

.choice:hover { border-color: #3d5266; background: var(--panel-2); }

.choice.selected {
  border-color: var(--accent);
  background: #16303f;
}

.choice .title { font-size: 17px; font-weight: 600; margin-bottom: 4px; }

.choice .sub { font-size: 13.5px; color: var(--muted); }

.choice .meta { font-size: 13px; color: var(--accent); margin-top: 8px; }

/* ---------- exam runner ---------- */

.exam-bar {
  position: sticky;
  top: 63px;
  z-index: 15;
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 12px 18px;
  display: flex;
  align-items: center;
  gap: 18px;
  flex-wrap: wrap;
  margin-bottom: 20px;
}

.exam-bar .stat { font-size: 14px; color: var(--muted); }
.exam-bar .stat b { color: var(--text); font-size: 16px; }

.progress-track {
  flex: 1 1 180px;
  height: 7px;
  background: #0b1219;
  border-radius: 4px;
  overflow: hidden;
  min-width: 120px;
}

.progress-fill {
  height: 100%;
  width: 0;
  background: var(--accent);
  transition: width .2s;
}

.q {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 20px;
  margin: 0 0 16px;
}

.q .qhead {
  display: flex;
  gap: 10px;
  align-items: baseline;
  margin-bottom: 12px;
  flex-wrap: wrap;
}

.q .qid {
  font-size: 12.5px;
  font-weight: 700;
  color: var(--accent);
  background: #16303f;
  border-radius: 5px;
  padding: 2px 8px;
  letter-spacing: .4px;
}

.q .qsec { font-size: 12.5px; color: var(--muted); }

.q .stem { font-size: 16px; margin-bottom: 14px; }

.opts { display: flex; flex-direction: column; gap: 8px; }

.opt {
  display: flex;
  gap: 11px;
  align-items: flex-start;
  padding: 11px 14px;
  border: 1px solid var(--line);
  border-radius: 8px;
  cursor: pointer;
  background: #131c26;
  transition: border-color .12s, background .12s;
}

.opt:hover { border-color: #3d5266; }

.opt input { margin: 3px 0 0; accent-color: var(--accent); flex: none; }

.opt .letter {
  font-weight: 700;
  color: var(--muted);
  flex: none;
  width: 15px;
}

.opt.picked { border-color: var(--accent); background: #16303f; }

.opt.correct { border-color: var(--ok); background: var(--ok-bg); }
.opt.correct .letter { color: var(--ok); }

.opt.wrong { border-color: var(--bad); background: var(--bad-bg); }
.opt.wrong .letter { color: var(--bad); }

.opt .mark { margin-left: auto; font-size: 13px; font-weight: 700; flex: none; }
.opt.correct .mark { color: var(--ok); }
.opt.wrong .mark { color: var(--bad); }

.explain {
  margin-top: 14px;
  padding: 12px 15px;
  border-radius: 8px;
  background: #131c26;
  border-left: 3px solid var(--accent);
  font-size: 14.5px;
}

.explain .ref {
  display: inline-block;
  margin-top: 7px;
  font-size: 13px;
  color: var(--muted);
}

.explain .ref b { color: var(--accent); }

/* ---------- results ---------- */

.score-hero {
  text-align: center;
  padding: 34px 20px;
  border-radius: var(--radius);
  border: 1px solid var(--line);
  background: var(--panel);
  margin-bottom: 22px;
}

.score-hero .pct { font-size: 58px; font-weight: 700; line-height: 1; }

.score-hero .verdict { font-size: 21px; font-weight: 600; margin-top: 12px; }

.score-hero.pass { border-color: var(--ok); background: linear-gradient(180deg, #12301c, var(--panel)); }
.score-hero.pass .pct, .score-hero.pass .verdict { color: var(--ok); }

.score-hero.fail { border-color: var(--bad); background: linear-gradient(180deg, #3a1618, var(--panel)); }
.score-hero.fail .pct, .score-hero.fail .verdict { color: var(--bad); }

.score-hero .detail { color: var(--muted); margin-top: 10px; font-size: 15px; }

.stat-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  gap: 12px;
  margin: 18px 0;
}

.stat-box {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: 8px;
  padding: 14px;
  text-align: center;
}

.stat-box .v { font-size: 25px; font-weight: 700; }
.stat-box .k { font-size: 12.5px; color: var(--muted); text-transform: uppercase; letter-spacing: .5px; margin-top: 3px; }

.stat-box.ok .v { color: var(--ok); }
.stat-box.bad .v { color: var(--bad); }

.breakdown { margin: 22px 0; }

.bar-row { display: flex; align-items: center; gap: 12px; margin: 7px 0; font-size: 14px; }

.bar-row .label { flex: 0 0 210px; color: var(--muted); }

.bar-track { flex: 1; height: 18px; background: #0b1219; border-radius: 4px; overflow: hidden; }

.bar-fill { height: 100%; background: var(--accent); }

.bar-row .num { flex: 0 0 62px; text-align: right; color: var(--muted); font-variant-numeric: tabular-nums; }

.review-head {
  display: flex;
  align-items: center;
  gap: 12px;
  margin: 30px 0 14px;
  flex-wrap: wrap;
}

.review-head h2 { margin: 0; }

.pill {
  font-size: 12.5px;
  padding: 3px 10px;
  border-radius: 20px;
  border: 1px solid var(--line);
  color: var(--muted);
}

.pill.bad { border-color: var(--bad); color: var(--bad); }
.pill.ok { border-color: var(--ok); color: var(--ok); }

.actions { display: flex; gap: 10px; flex-wrap: wrap; margin: 22px 0; }

.hidden { display: none !important; }

/* ---------- study guide layout ---------- */

.layout {
  display: grid;
  grid-template-columns: 268px minmax(0, 1fr);
  gap: 34px;
  align-items: start;
}

.sidebar { position: sticky; top: 84px; }

.sidebar-inner {
  max-height: calc(100vh - 110px);
  overflow-y: auto;
  border: 1px solid var(--line);
  border-radius: var(--radius);
  background: var(--panel);
  padding: 14px 10px 18px;
}

.sidebar-title {
  font-size: 12px;
  text-transform: uppercase;
  letter-spacing: .8px;
  color: var(--muted);
  padding: 0 10px 10px;
  border-bottom: 1px solid var(--line);
  margin-bottom: 8px;
}

ul.toc { list-style: none; padding: 0; margin: 0; }

ul.toc li { margin: 0; }

ul.toc a {
  display: block;
  text-decoration: none;
  color: var(--muted);
  font-size: 13.5px;
  padding: 5px 10px;
  border-radius: 6px;
  border-left: 2px solid transparent;
  line-height: 1.35;
}

ul.toc a:hover { color: var(--text); background: var(--panel-2); }

ul.toc li.l1 > a {
  color: var(--text);
  font-weight: 600;
  font-size: 14px;
  margin-top: 10px;
  border-left-color: var(--accent);
}

ul.toc li.l2 > a { padding-left: 20px; }

.content { min-width: 0; }

.content h1 {
  font-size: 27px;
  margin: 40px 0 14px;
  padding-bottom: 10px;
  border-bottom: 1px solid var(--line);
}

.content h1:first-child { margin-top: 0; }

.content h2 {
  font-size: 21px;
  margin: 34px 0 12px;
  color: var(--accent);
}

.content h3 {
  font-size: 17px;
  margin: 26px 0 10px;
  color: var(--text);
}

.content h4 { font-size: 15px; margin: 20px 0 8px; color: var(--muted); }

.content hr { border: 0; border-top: 1px solid var(--line); margin: 30px 0; }

.tablewrap { overflow-x: auto; margin: 14px 0; }

.mathblock {
  overflow-x: auto;
  padding: 6px 0;
  margin: 12px 0;
}

.content .note { margin: 16px 0; }

@media (max-width: 900px) {
  .layout { grid-template-columns: 1fr; gap: 20px; }
  .sidebar { position: static; }
  .sidebar-inner { max-height: 260px; }
}

/* ---------- print ---------- */

@media print {
  :root {
    --bg: #fff;
    --panel: #fff;
    --panel-2: #f4f6f8;
    --line: #c8d0d8;
    --text: #111;
    --muted: #555;
    --accent: #0b5f86;
    --ok: #1a7f37;
    --bad: #b3261e;
    --ok-bg: #eaf7ee;
    --bad-bg: #fdecea;
  }

  body { background: #fff; color: #111; font-size: 11.5pt; }

  header.site, footer.site, .actions, .exam-bar, .sidebar,
  #setup, #filterAll, #filterWrong, .review-head .pill { display: none !important; }

  main { max-width: none; padding: 0; }

  .layout { display: block; }

  .q, .card, .score-hero, .stat-box {
    break-inside: avoid;
    page-break-inside: avoid;
    border: 1px solid #c8d0d8;
    box-shadow: none;
  }

  .score-hero { padding: 18px; }
  .score-hero .pct { font-size: 34pt; }

  .opt { background: #fff; }
  .opt.correct { background: #eaf7ee; }
  .opt.wrong { background: #fdecea; }

  .explain { background: #f4f6f8; }

  a { color: #111; text-decoration: none; }

  .tablewrap { overflow: visible; }
  table { font-size: 9.5pt; }
  th { background: #f4f6f8; }

  .mathblock { overflow: visible; }
}

footer.site {
  border-top: 1px solid var(--line);
  padding: 22px 24px;
  color: var(--muted);
  font-size: 13.5px;
  text-align: center;
}

@media (max-width: 620px) {
  .exam-bar { top: 0; }
  .bar-row .label { flex-basis: 130px; font-size: 13px; }
  .score-hero .pct { font-size: 44px; }
  main { padding: 20px 14px 60px; }
}

/* ---------- question pool (standalone HTML) ---------- */
.partnote {
  color: var(--muted);
  font-size: 14px;
  margin: -4px 0 22px;
}

.qpool {
  background: var(--panel);
  border: 1px solid var(--line);
  border-radius: var(--radius);
  padding: 16px 18px;
  margin: 14px 0;
  break-inside: avoid;
}

.qpool .qhead {
  display: flex;
  align-items: baseline;
  gap: 10px;
  margin-bottom: 8px;
}

.qpool .qid {
  font-weight: 700;
  color: var(--accent);
  font-variant-numeric: tabular-nums;
}

.qpool .qsec {
  font-size: 12.5px;
  color: var(--muted);
}

.qpool .stem { font-size: 16px; margin-bottom: 12px; }

.qpool ul.opts {
  list-style: none;
  padding: 0;
  margin: 0 0 12px;
  display: flex;
  flex-direction: column;
  gap: 6px;
}

.qpool ul.opts li.opt {
  display: flex;
  align-items: flex-start;
  gap: 10px;
  padding: 8px 12px;
  border: 1px solid var(--line);
  border-radius: 8px;
  background: var(--panel-2);
  font-size: 15px;
}

.qpool ul.opts li.opt .letter {
  flex: none;
  width: 20px;
  font-weight: 700;
  color: var(--muted);
}

.qpool ul.opts li.opt .otext { flex: 1; }

.qpool ul.opts li.opt.correct {
  border-color: var(--ok);
  background: var(--ok-bg);
}

.qpool ul.opts li.opt.correct .letter { color: var(--ok); }

.qpool ul.opts li.opt .mark {
  flex: none;
  color: var(--ok);
  font-weight: 700;
}

.qpool details.answer { margin-top: 4px; }

.qpool details.answer > summary {
  cursor: pointer;
  color: var(--accent);
  font-size: 14px;
  font-weight: 600;
  padding: 4px 0;
  list-style: none;
}

.qpool details.answer > summary::-webkit-details-marker { display: none; }

.qpool details.answer > summary::before {
  content: "▸ ";
  display: inline-block;
  transition: transform .15s;
}

.qpool details.answer[open] > summary::before { content: "▾ "; }

.qpool details.answer .explain {
  margin-top: 8px;
  padding: 12px 14px;
  border-left: 3px solid var(--accent);
  background: var(--panel-2);
  border-radius: 0 8px 8px 0;
  font-size: 14.5px;
}

.qpool details.answer .explain .ref {
  margin-top: 8px;
  font-size: 13px;
  color: var(--muted);
}

.qpool details.answer .explain .ref b { color: var(--accent); }

@media print {
  .qpool { break-inside: avoid; page-break-inside: avoid; border: 1px solid #c8d0d8; }
  .qpool details.answer { display: block; }
  .qpool details.answer > summary { display: none; }
  .qpool details.answer > .explain { display: block !important; }
  .qpool ul.opts li.opt { background: #fff; }
  .qpool ul.opts li.opt.correct { background: #eaf7ee; }
}