/* Layout: graph-paper ground, one centred column. Home is a two-column grid of topic cards; a round is a single question sheet. */
:root {
  --bg: #F1F4F8;
  --grid: rgba(30, 60, 120, 0.07);
  --surface: #FFFFFF;
  --ink: #101A2B;
  --muted: #586479;
  --line: #D3DAE6;
  --accent: #1B3FD8;
  --accent-ink: #FFFFFF;
  --accent-soft: #E6ECFF;
  --good: #0F7B58;
  --good-bg: #E2F4EC;
  --bad: #B3302A;
  --bad-bg: #FBE8E5;
  --display: "Bricolage Grotesque", system-ui, -apple-system, "Segoe UI", sans-serif;
  --math: "STIX Two Text", "Cambria Math", "Times New Roman", serif;
  --mono: "IBM Plex Mono", ui-monospace, Menlo, Consolas, monospace;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #0E1420;
    --grid: rgba(140, 170, 255, 0.07);
    --surface: #161E2D;
    --ink: #E8EDF7;
    --muted: #93A0B8;
    --line: #2A3550;
    --accent: #8CA0FF;
    --accent-ink: #0E1420;
    --accent-soft: #1C2745;
    --good: #4CC9A0;
    --good-bg: #12302A;
    --bad: #FF8F80;
    --bad-bg: #3A1B19;
    color-scheme: dark;
  }
}
:root[data-theme="dark"] {
  --bg: #0E1420;
  --grid: rgba(140, 170, 255, 0.07);
  --surface: #161E2D;
  --ink: #E8EDF7;
  --muted: #93A0B8;
  --line: #2A3550;
  --accent: #8CA0FF;
  --accent-ink: #0E1420;
  --accent-soft: #1C2745;
  --good: #4CC9A0;
  --good-bg: #12302A;
  --bad: #FF8F80;
  --bad-bg: #3A1B19;
  color-scheme: dark;
}

* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body {
  background-color: var(--bg);
  background-image:
    linear-gradient(var(--grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--grid) 1px, transparent 1px);
  background-size: 28px 28px;
  color: var(--ink);
  font-family: var(--display);
  font-size: 16px;
  line-height: 1.5;
}
button { font: inherit; color: inherit; cursor: pointer; }
:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
sup, sub { font-size: 0.72em; line-height: 0; }

.wrap {
  max-width: 920px;
  margin: 0 auto;
  padding-block: 32px 64px;
  padding-left: max(16px, env(safe-area-inset-left, 0px));
  padding-right: max(16px, env(safe-area-inset-right, 0px));
}
.vh { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; }

/* ---------- Home ---------- */
.eyebrow { font-family: var(--mono); font-size: 0.78rem; letter-spacing: 0.12em; text-transform: uppercase; color: var(--accent); margin: 0 0 12px; }
h1 { font-family: var(--display); font-weight: 700; font-size: clamp(2.1rem, 6vw, 3.4rem); line-height: 1.05; letter-spacing: -0.02em; margin: 0 0 14px; text-wrap: balance; }
.lead { font-family: var(--math); font-size: 1.2rem; color: var(--muted); max-width: 56ch; margin: 0 0 28px; }

.controls { display: flex; flex-wrap: wrap; align-items: center; gap: 12px 16px; margin-bottom: 20px; }
.controls .lbl { font-family: var(--mono); font-size: 0.78rem; letter-spacing: 0.08em; text-transform: uppercase; color: var(--muted); }
.seg { display: inline-flex; border: 1px solid var(--line); border-radius: 8px; background: var(--surface); padding: 3px; gap: 3px; }
.seg label { position: relative; }
.seg input { position: absolute; opacity: 0; inset: 0; margin: 0; cursor: pointer; }
.seg span { display: block; padding: 7px 14px; border-radius: 5px; font-weight: 500; font-size: 0.95rem; color: var(--muted); }
.seg input:checked + span { background: var(--accent); color: var(--accent-ink); }
.seg input:focus-visible + span { outline: 3px solid var(--accent); outline-offset: 2px; }

.topics { display: grid; grid-template-columns: minmax(0, 1fr); gap: 12px; }
@media (min-width: 640px) { .topics { grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; } }
.topic {
  display: flex; flex-direction: column; gap: 6px; text-align: left;
  background: var(--surface); border: 1px solid var(--line); border-radius: 10px;
  padding: 18px 18px 16px; min-width: 0;
  transition: border-color 0.15s, transform 0.15s;
}
.topic:hover { border-color: var(--accent); transform: translateY(-1px); }
.topic .glyph { font-family: var(--math); font-size: 1.5rem; color: var(--accent); line-height: 1.3; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.topic .name { font-weight: 700; font-size: 1.18rem; letter-spacing: -0.01em; }
.topic .blurb { color: var(--muted); font-size: 0.93rem; }
.topic .meta { margin-top: auto; padding-top: 12px; display: flex; justify-content: space-between; gap: 8px; font-family: var(--mono); font-size: 0.76rem; color: var(--muted); font-variant-numeric: tabular-nums; }
.topic .meta .best { color: var(--good); }

/* ---------- Quiz ---------- */
.bar { display: flex; align-items: center; justify-content: space-between; gap: 12px; flex-wrap: wrap; margin-bottom: 14px; }
.back { border: 1px solid var(--line); background: var(--surface); border-radius: 8px; padding: 7px 12px; font-size: 0.92rem; font-weight: 500; }
.back:hover { border-color: var(--accent); }
.stats { font-family: var(--mono); font-size: 0.82rem; color: var(--muted); display: flex; gap: 16px; font-variant-numeric: tabular-nums; }
.stats b { color: var(--ink); font-weight: 500; }
.topic-title { font-weight: 700; font-size: 1.05rem; letter-spacing: -0.01em; margin: 0 0 10px; }
.track { height: 6px; background: var(--line); border-radius: 3px; overflow: hidden; margin-bottom: 22px; }
.fill { height: 100%; background: var(--accent); border-radius: 3px; transition: width 0.25s; }

.sheet { background: var(--surface); border: 1px solid var(--line); border-radius: 12px; padding: clamp(18px, 4vw, 30px); }
.qnum { font-family: var(--mono); font-size: 0.78rem; letter-spacing: 0.1em; text-transform: uppercase; color: var(--muted); margin: 0 0 10px; }
.qtext { font-family: var(--math); font-size: clamp(1.28rem, 3.4vw, 1.6rem); line-height: 1.38; margin: 0 0 22px; text-wrap: pretty; }
.opts { display: grid; gap: 10px; margin: 0; padding: 0; list-style: none; }
.opt {
  display: grid; grid-template-columns: 30px minmax(0, 1fr); gap: 12px; align-items: start; width: 100%;
  text-align: left; background: var(--bg); border: 1.5px solid var(--line); border-radius: 9px; padding: 12px 14px;
  transition: border-color 0.12s, background 0.12s;
}
.opt .ltr { font-family: var(--mono); font-size: 0.85rem; font-weight: 500; width: 28px; height: 28px; border-radius: 6px; border: 1.5px solid var(--line); display: grid; place-items: center; color: var(--muted); background: var(--surface); }
.opt .txt { font-family: var(--math); font-size: 1.18rem; line-height: 1.4; padding-top: 2px; overflow-wrap: anywhere; }
.opt:hover:not([disabled]) { border-color: var(--accent); }
.opt:hover:not([disabled]) .ltr { border-color: var(--accent); color: var(--accent); }
.opt[disabled] { cursor: default; }
.opt.good { border-color: var(--good); background: var(--good-bg); }
.opt.good .ltr { background: var(--good); border-color: var(--good); color: var(--bg); }
.opt.bad { border-color: var(--bad); background: var(--bad-bg); }
.opt.bad .ltr { background: var(--bad); border-color: var(--bad); color: var(--bg); }
.opt.dim { opacity: 0.6; }

.fb { margin-top: 20px; border-radius: 9px; padding: 16px 18px; border: 1.5px solid var(--line); background: var(--bg); }
.fb.good { border-color: var(--good); background: var(--good-bg); }
.fb.bad { border-color: var(--bad); background: var(--bad-bg); }
.fb .verdict { font-weight: 700; font-size: 1rem; margin: 0 0 6px; }
.fb.good .verdict { color: var(--good); }
.fb.bad .verdict { color: var(--bad); }
.fb .why { font-family: var(--math); font-size: 1.08rem; line-height: 1.5; margin: 0; }
.actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 18px; }
.btn { border-radius: 9px; padding: 11px 20px; font-weight: 700; border: 1.5px solid var(--accent); background: var(--accent); color: var(--accent-ink); }
.btn:hover { filter: brightness(1.08); }
.btn.ghost { background: transparent; color: var(--accent); }
.btn.ghost:hover { background: var(--accent-soft); filter: none; }
.hint { display: none; font-family: var(--mono); font-size: 0.74rem; color: var(--muted); margin: 14px 0 0; }
@media (hover: hover) { .hint { display: block; } }

/* ---------- Results ---------- */
.score { display: flex; flex-wrap: wrap; align-items: baseline; gap: 6px 22px; margin: 4px 0 6px; }
.pct { font-weight: 700; font-size: clamp(3.6rem, 14vw, 6rem); line-height: 1; letter-spacing: -0.04em; color: var(--accent); font-variant-numeric: tabular-nums; }
.score .of { font-family: var(--mono); font-size: 0.95rem; color: var(--muted); }
.verdict-line { font-family: var(--math); font-size: 1.25rem; margin: 6px 0 4px; }
.pb { font-family: var(--mono); font-size: 0.8rem; color: var(--good); margin: 0 0 4px; }
.review { margin-top: 34px; }
.review h2 { font-size: 1.25rem; letter-spacing: -0.01em; margin: 0 0 14px; }
.miss { background: var(--surface); border: 1px solid var(--line); border-radius: 10px; padding: 16px 18px; margin-bottom: 12px; }
.miss .mq { font-family: var(--math); font-size: 1.15rem; margin: 0 0 10px; }
.miss .row { font-family: var(--math); font-size: 1.05rem; margin: 4px 0; overflow-wrap: anywhere; }
.miss .tag { font-family: var(--mono); font-size: 0.72rem; letter-spacing: 0.08em; text-transform: uppercase; margin-right: 8px; }
.miss .you .tag { color: var(--bad); }
.miss .ans .tag { color: var(--good); }
.miss .mwhy { font-family: var(--math); font-size: 1rem; color: var(--muted); margin: 10px 0 0; }
.clean { font-family: var(--math); font-size: 1.1rem; color: var(--muted); }

@media (prefers-reduced-motion: reduce) {
  .fill, .topic, .opt { transition: none; }
  .topic:hover { transform: none; }
}

form { margin: 0; }
.opts form, .opts { margin: 0; }