/* Layout: question sheet on the left, OMR-style answer sheet (phiếu trả lời) docked on the right; stacks on phones. */
:root {
  --bg: #f3f4f1;
  --paper: #fdfdfb;
  --ink: #1d2733;
  --muted: #5f6b76;
  --line: #d8dcd6;
  --accent: #1f5f8b;
  --accent-soft: #e2edf5;
  --ok: #1e7a4c;
  --ok-soft: #e0f2e8;
  --bad: #b3362f;
  --bad-soft: #f8e3e0;
  --warn: #a8660b;
  --warn-soft: #f8ecd7;
  --figure: #ffffff;
  --font-display: "Lexend", "Be Vietnam Pro", system-ui, sans-serif;
  --font-body: "Be Vietnam Pro", system-ui, -apple-system, "Segoe UI", sans-serif;
  --font-mono: "JetBrains Mono", ui-monospace, "SFMono-Regular", Menlo, monospace;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #12171c; --paper: #1a2128; --ink: #e4e8ea; --muted: #97a3ad; --line: #2e3842;
    --accent: #6fb0dd; --accent-soft: #1d3446; --ok: #5cc68d; --ok-soft: #173326;
    --bad: #f07f76; --bad-soft: #3a1f1d; --warn: #e2a64b; --warn-soft: #3a2c16; --figure: #f4f4f2; color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #12171c; --paper: #1a2128; --ink: #e4e8ea; --muted: #97a3ad; --line: #2e3842;
  --accent: #6fb0dd; --accent-soft: #1d3446; --ok: #5cc68d; --ok-soft: #173326;
  --bad: #f07f76; --bad-soft: #3a1f1d; --warn: #e2a64b; --warn-soft: #3a2c16; --figure: #f4f4f2; color-scheme: dark;
}
* { box-sizing: border-box; }
[hidden] { display: none !important; }
img { max-width: 100%; }
body {
  margin: 0; background: var(--bg); color: var(--ink);
  font: 16px/1.6 var(--font-body);
  padding-inline: 16px; padding-block: 0 48px;
}
.wrap { max-width: 1120px; margin: 0 auto; }

header.top {
  display: flex; flex-wrap: wrap; align-items: flex-end; justify-content: space-between; gap: 16px;
  padding-block: 28px 20px; border-bottom: 2px solid var(--ink); margin-bottom: 24px;
}
.eyebrow { font: 600 12px/1.5 var(--font-body); letter-spacing: .12em; text-transform: uppercase; color: var(--muted); }
h1 { font: 700 clamp(26px, 4vw, 36px)/1.15 var(--font-display); margin: 8px 0 4px; text-wrap: balance; letter-spacing: -.01em; }
.sub { color: var(--muted); font-size: 14px; margin: 0; }
.stats { display: flex; gap: 20px; font-variant-numeric: tabular-nums; }
.stat { display: grid; gap: 2px; }
.stat b { font: 600 24px/1 var(--font-display); }
.stat span { font-size: 12px; color: var(--muted); letter-spacing: .04em; }
.stat.ok b { color: var(--ok); } .stat.bad b { color: var(--bad); }

.layout { display: grid; grid-template-columns: minmax(0, 1fr) 300px; gap: 28px; align-items: start; }
@media (max-width: 860px) { .layout { grid-template-columns: minmax(0, 1fr); } }

/* Question */
.card { background: var(--paper); border: 1px solid var(--line); border-radius: 6px; padding: clamp(18px, 3vw, 32px); min-width: 0; }
.qhead { display: flex; align-items: baseline; justify-content: space-between; gap: 12px; margin-bottom: 14px; }
.qnum { font: 700 22px/1 var(--font-display); color: var(--accent); }
.qnum small { font: 500 14px var(--font-body); color: var(--muted); margin-left: 6px; }
.qtext { font-size: 17px; max-width: 68ch; }
.qtext ol, .qtext ul { padding-left: 1.4em; margin: .5em 0; }
.qtext figure { margin: 14px 0; }
.qtext img, .opt img { display: block; background: var(--figure); border-radius: 4px; padding: 6px; max-width: 100%; height: auto; }
.qtext pre { font: 14px/1.5 var(--font-mono); background: var(--accent-soft); padding: 12px 14px; border-radius: 4px; overflow-x: auto; }
code { font-family: var(--font-mono); font-size: .88em; background: var(--accent-soft); padding: 1px 5px; border-radius: 3px; }
.formula { text-align: center; font-size: 18px; margin: 12px 0; }
.frac { display: inline-flex; flex-direction: column; vertical-align: middle; text-align: center; font-size: .9em; margin: 0 2px; }
.frac > span:first-child { border-bottom: 1px solid currentColor; padding: 0 3px; }
.tbl { overflow-x: auto; margin: 12px 0; }
table { border-collapse: collapse; font-variant-numeric: tabular-nums; font-size: 15px; }
th, td { border: 1px solid var(--line); padding: 5px 12px; text-align: center; }
th { background: var(--accent-soft); font-weight: 600; }

.opts { display: grid; gap: 10px; margin-top: 20px; }
.opt {
  display: grid; grid-template-columns: 34px minmax(0, 1fr); gap: 12px; align-items: start;
  width: 100%; text-align: left; font: inherit; color: inherit; cursor: pointer;
  background: var(--paper); border: 1.5px solid var(--line); border-radius: 6px; padding: 10px 14px;
  transition: border-color .15s, background-color .15s;
}
.opt:hover:not(:disabled) { border-color: var(--accent); }
.opt:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
.opt:disabled { cursor: default; }
.bubble {
  width: 30px; height: 30px; border-radius: 50%; border: 1.5px solid var(--muted);
  display: grid; place-items: center; font: 600 14px var(--font-display); color: var(--muted);
}
.opt .body { padding-top: 3px; min-width: 0; }
.opt.correct { border-color: var(--ok); background: var(--ok-soft); }
.opt.correct .bubble { background: var(--ok); border-color: var(--ok); color: var(--paper); }
.opt.wrong { border-color: var(--bad); background: var(--bad-soft); }
.opt.wrong .bubble { background: var(--bad); border-color: var(--bad); color: var(--paper); }
.opt.dim { opacity: .55; }
.opt.picked { border-color: var(--accent); background: var(--accent-soft); }
.opt.picked .bubble { background: var(--accent); border-color: var(--accent); color: var(--paper); }
.opt.missed { border-style: dashed; background: transparent; }
.opt.missed .bubble { background: transparent; color: var(--ok); }
.opt .tag { display: block; font-size: 12px; font-weight: 600; color: var(--ok); margin-top: 2px; }
.multi-hint { font-size: 14px; color: var(--muted); margin: 16px 0 -8px; }
.submit-row { display: flex; justify-content: flex-end; margin-top: 12px; }
.verdict.part h3 { color: var(--warn); }
.cell.part { background: var(--warn); border-color: var(--warn); color: var(--paper); }
.legend .lpart { background: var(--warn); border-color: var(--warn); }

.verdict { margin-top: 20px; border-top: 1px dashed var(--line); padding-top: 18px; }
.verdict h3 { font: 600 17px/1.3 var(--font-display); margin: 0 0 8px; display: flex; align-items: center; gap: 8px; }
.verdict.ok h3 { color: var(--ok); } .verdict.bad h3 { color: var(--bad); }
.verdict .ans { font-weight: 600; }
.verdict p { margin: 0; max-width: 68ch; }
.verdict p.src { margin-top: 10px; font-size: 13px; color: var(--muted); }
.exams { display: flex; flex-wrap: wrap; gap: 8px; margin-bottom: 20px; }
.exam {
  font: 600 14px var(--font-body); padding: 8px 14px; border-radius: 999px; cursor: pointer;
  border: 1.5px solid var(--line); background: var(--paper); color: var(--ink);
}
.exam:hover { border-color: var(--accent); }
.exam[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: var(--paper); }
.exam:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }

.nav { display: flex; flex-wrap: wrap; justify-content: space-between; gap: 10px; margin-top: 24px; }
.btn {
  font: 600 14px var(--font-body); padding: 10px 18px; border-radius: 6px; cursor: pointer;
  border: 1.5px solid var(--ink); background: transparent; color: var(--ink);
}
.btn.primary { background: var(--ink); color: var(--paper); }
.btn:disabled { opacity: .35; cursor: default; }
.btn:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
.hint { font-size: 12px; color: var(--muted); margin-top: 14px; }
kbd { font: 600 11px var(--font-mono); border: 1px solid var(--line); border-bottom-width: 2px; border-radius: 3px; padding: 0 4px; }

/* Answer sheet */
aside.sheet { position: sticky; top: calc(env(safe-area-inset-top, 0px) + 16px); background: var(--paper); border: 1px solid var(--line); border-radius: 6px; padding: 18px; }
@media (max-width: 860px) { aside.sheet { position: static; } }
.sheet h2 { font: 600 15px var(--font-display); margin: 0 0 4px; }
.sheet .sub { margin-bottom: 12px; }
.grid { display: grid; grid-template-columns: repeat(10, minmax(0, 1fr)); gap: 4px; }
.cell {
  aspect-ratio: 1; max-width: 100%; border-radius: 50%; border: 1.2px solid var(--line); background: transparent;
  font: 500 10px/1 var(--font-mono); color: var(--muted); cursor: pointer; padding: 0;
  font-variant-numeric: tabular-nums;
}
.cell:hover { border-color: var(--accent); color: var(--ink); }
.cell:focus-visible { outline: 2px solid var(--accent); outline-offset: 1px; }
.cell.ok { background: var(--ok); border-color: var(--ok); color: var(--paper); }
.cell.bad { background: var(--bad); border-color: var(--bad); color: var(--paper); }
.cell.cur { box-shadow: 0 0 0 2px var(--paper), 0 0 0 4px var(--accent); }
.cell.hide { opacity: .15; }
.legend { display: flex; flex-wrap: wrap; gap: 12px; font-size: 12px; color: var(--muted); margin-top: 12px; }
.legend i { display: inline-block; width: 10px; height: 10px; border-radius: 50%; margin-right: 5px; vertical-align: -1px; border: 1px solid var(--line); }
.legend .lok { background: var(--ok); border-color: var(--ok); } .legend .lbad { background: var(--bad); border-color: var(--bad); }
.tools { display: grid; gap: 8px; margin-top: 16px; }
.tools label { display: flex; gap: 8px; align-items: center; font-size: 14px; cursor: pointer; }
.tools .btn { width: 100%; }
.confirm { display: grid; gap: 8px; font-size: 13px; background: var(--bad-soft); padding: 10px; border-radius: 6px; }
.confirm div { display: flex; gap: 8px; }
.confirm .btn { padding: 6px 10px; }
.note { font-size: 12px; color: var(--muted); margin-top: 14px; line-height: 1.5; }
@media (prefers-reduced-motion: reduce) { * { transition: none !important; } }
.exam-group { display: contents; }
a.exam { text-decoration: none; display: inline-flex; align-items: center; }
.essay-link { border-style: dashed; }

/* Nhãn nhóm chủ đề ở góc phải đầu câu */
.qhead .time { font-size: 13px; color: var(--muted); }
.gcount { font-weight: 400; opacity: .7; margin-left: 5px; font-size: 12.5px; }
.sheet .grid { grid-template-columns: repeat(10, minmax(0, 1fr)); }
.verdict .ans { color: var(--accent); }