:root {
  --ink: #1c2430; --muted: #5b6676; --line: #d8dee6; --bg: #f7f8fa; --card: #ffffff;
  --accent: #1f5fae; --good: #1d7a46; --good-bg: #e8f5ee; --bad: #b3261e; --bad-bg: #fbeceb; --flag: #b7791f;
}
* { box-sizing: border-box; }
/* Hides a label from sight while leaving it in the accessibility tree. */
.sr-only { position: absolute; width: 1px; height: 1px; margin: -1px; padding: 0; overflow: hidden; clip: rect(0 0 0 0); white-space: nowrap; border: 0; }
body { margin: 0; font: 17px/1.55 system-ui, -apple-system, "Segoe UI", sans-serif; color: var(--ink); background: var(--bg); }
a { color: var(--accent); }
h1 { font-size: 1.6rem; margin: 0.4em 0; }
h2 { font-size: 1.2rem; margin: 0.2em 0 0.6em; }
.page { max-width: 760px; margin: 0 auto; padding: 16px; width: 100%; }
.bar { display: flex; gap: 16px; align-items: center; padding: 10px 16px; background: var(--ink); color: #fff; position: sticky; top: 0; z-index: 2; }
.bar .brand { color: #fff; font-weight: 600; text-decoration: none; margin-right: auto; }
.strip { display: flex; gap: 6px; padding: 10px 16px; overflow-x: auto; background: var(--card); border-bottom: 1px solid var(--line); }
.dot { min-width: 34px; height: 34px; border-radius: 17px; border: 1px solid var(--line); background: var(--card); font: inherit; font-size: 0.85rem; cursor: pointer; }
.dot.current { outline: 2px solid var(--accent); outline-offset: 1px; }
.dot.right { background: var(--good-bg); border-color: var(--good); color: var(--good); }
.dot.wrong { background: var(--bad-bg); border-color: var(--bad); color: var(--bad); }
.dot.flagged { box-shadow: inset 0 -4px 0 var(--flag); }
.layout { display: flex; align-items: flex-start; justify-content: center; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 20px; margin: 16px 0; }
.card-head { display: flex; justify-content: space-between; align-items: center; gap: 12px; margin-bottom: 8px; }
.concept { color: var(--muted); font-size: 0.9rem; }
.stem { font-size: 1.05rem; margin: 8px 0 16px; overflow-x: auto; }
.stem table, .notes table { border-collapse: collapse; margin: 8px 0; }
.stem td, .stem th, .notes td, .notes th { border: 1px solid var(--line); padding: 4px 10px; }
.figure { max-width: 100%; height: auto; display: block; margin: 8px auto 16px; }
.part { border: 0; padding: 0; margin: 0 0 16px; min-width: 0; }
.prompt { margin: 0 0 8px; font-weight: 500; }
.part-label { color: var(--muted); }
.options { display: grid; gap: 8px; }
.option { display: flex; gap: 10px; align-items: flex-start; padding: 12px 14px; border: 1px solid var(--line); border-radius: 10px; cursor: pointer; }
.option:hover { border-color: var(--accent); }
.option:has(input:checked) { border-color: var(--accent); background: #eef4fc; }
.option input { margin-top: 5px; }
.numeric { font: inherit; padding: 10px 12px; border: 1px solid var(--line); border-radius: 10px; width: 12em; max-width: 100%; }
.btn { font: inherit; padding: 10px 16px; border-radius: 10px; border: 1px solid var(--line); background: var(--card); color: var(--ink); cursor: pointer; text-decoration: none; display: inline-block; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; }
.btn.ghost { padding: 4px 10px; font-size: 0.85rem; }
.btn.ghost.on { border-color: var(--flag); color: var(--flag); }
.btn:disabled { opacity: 0.45; cursor: default; }
.actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 12px; }
.hint, .warning { color: var(--muted); font-size: 0.9rem; }
.warning { background: #fff7e6; border: 1px solid #f0d9a8; border-radius: 10px; padding: 8px 12px; color: #6b4e16; }
.feedback-list { display: grid; gap: 8px; }
.fb { border: 1px solid var(--line); border-left-width: 5px; border-radius: 10px; padding: 10px 14px; }
.fb.right { border-left-color: var(--good); }
.fb.wrong { border-left-color: var(--line); }
.fb.right.chosen { background: var(--good-bg); }
.fb.wrong.chosen { background: var(--bad-bg); border-left-color: var(--bad); }
.fb-head { display: flex; justify-content: space-between; gap: 12px; font-weight: 600; }
.tag { font-size: 0.8rem; font-weight: 500; color: var(--muted); white-space: nowrap; }
.why { margin: 6px 0 0; color: #333c48; }
.verdict { font-weight: 700; font-size: 1.1rem; margin: 16px 0 4px; }
.verdict.right, td.right { color: var(--good); }
.verdict.wrong, td.wrong { color: var(--bad); }
.big-score { font-size: 2.4rem; font-weight: 700; margin: 0 0 8px; }
table.results { width: 100%; border-collapse: collapse; margin: 12px 0; }
table.results th, table.results td { text-align: left; padding: 8px 6px; border-bottom: 1px solid var(--line); }
.notes section { background: var(--card); border: 1px solid var(--line); border-radius: 10px; padding: 16px 20px; margin: 16px 0; }
.notes section:target { border-color: var(--accent); box-shadow: 0 0 0 3px rgba(31, 95, 174, 0.15); }
.trap { border-left: 4px solid var(--bad); padding-left: 12px; }
.notes-panel { width: 420px; flex: none; position: sticky; top: 60px; max-height: calc(100vh - 72px); overflow: auto; margin: 16px 16px 16px 0; background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 12px 16px; }
.notes-panel section { border: 0; padding: 0; margin: 8px 0; }
.notes-panel-head { display: flex; justify-content: space-between; align-items: center; gap: 8px; font-size: 0.9rem; }
.module-list { display: grid; gap: 12px; padding: 0; list-style: none; }
.module-card { display: flex; flex-wrap: wrap; align-items: center; gap: 12px; }
.module-card .grow { flex: 1 1 220px; }
.meter { height: 8px; border-radius: 4px; background: var(--line); overflow: hidden; }
.meter > span { display: block; height: 100%; background: var(--good); }
.meter.practicing > span { background: var(--accent); }
.status { font-size: 0.8rem; color: var(--muted); }
.concept-row { display: grid; grid-template-columns: 1fr 120px 90px; gap: 12px; align-items: center; padding: 8px 0; border-bottom: 1px solid var(--line); }
@media (max-width: 899px) { .notes-panel { display: none; } }
@media (max-width: 560px) {
  body { font-size: 16px; }
  .card { padding: 16px; border-radius: 10px; }
  .bar { gap: 10px; font-size: 0.9rem; }
  .concept-row { grid-template-columns: 1fr 80px; }
  .concept-row .status { grid-column: 1 / -1; }
}