:root {
  --bg: #fbfbf8; --fg: #1d1f24; --muted: #5b6070; --line: #d9dbe1; --card: #fff;
  --accent: #1f5fbf; --ok: #1b7a3d; --bad: #b3261e; --warn: #8a5a00; --chip: #eef1f7;
}
@media (prefers-color-scheme: dark) {
  :root { --bg: #15171c; --fg: #e8e9ec; --muted: #a3a8b6; --line: #343844; --card: #1d2027;
          --accent: #7fb0ff; --ok: #6fd08f; --bad: #ff8a80; --warn: #f0c060; --chip: #262a33; }
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--fg); font: 17px/1.6 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif; }
main, header.top, footer { max-width: 860px; margin: 0 auto; padding: 0 16px; }
header.top { display: flex; flex-wrap: wrap; gap: 8px 16px; align-items: center; justify-content: space-between; padding-top: 12px; padding-bottom: 12px; border-bottom: 1px solid var(--line); }
.brand { font-weight: 700; color: var(--fg); text-decoration: none; }
nav a { margin-left: 12px; }
a { color: var(--accent); }
footer { color: var(--muted); padding-top: 24px; padding-bottom: 32px; }
.skip { position: absolute; left: -999px; } .skip:focus { left: 8px; top: 8px; background: var(--card); padding: 4px 8px; }
h1 { font-size: 1.5rem; line-height: 1.3; } h2 { font-size: 1.25rem; margin-top: 2rem; } h3 { font-size: 1.05rem; }
.filters { display: flex; flex-wrap: wrap; gap: 8px; margin: 12px 0; }
.filters select, .filters input { font: inherit; padding: 6px 8px; border: 1px solid var(--line); border-radius: 6px; background: var(--card); color: var(--fg); min-width: 0; }
.filters input { flex: 1 1 200px; }
.cards { list-style: none; padding: 0; display: grid; gap: 10px; }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 8px; padding: 12px 14px; }
.card .meta, .muted { color: var(--muted); font-size: .9rem; }
.chip { display: inline-block; background: var(--chip); border-radius: 999px; padding: 0 8px; font-size: .8rem; margin-right: 4px; }
.chip.draft { background: transparent; border: 1px dashed var(--warn); color: var(--warn); }
.q { background: var(--card); border: 1px solid var(--line); border-radius: 8px; padding: 12px 14px; margin: 14px 0; }
.q header { display: flex; flex-wrap: wrap; gap: 4px 8px; align-items: baseline; }
.q .qid { font-weight: 700; }
.answer-row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 10px 0; }
.answer-row input[type=text] { font: inherit; padding: 6px 8px; width: 12em; max-width: 100%; border: 1px solid var(--line); border-radius: 6px; background: var(--bg); color: var(--fg); }
button { font: inherit; padding: 6px 12px; border-radius: 6px; border: 1px solid var(--line); background: var(--chip); color: var(--fg); cursor: pointer; }
button.primary { background: var(--accent); color: #fff; border-color: var(--accent); }
@media (prefers-color-scheme: dark) { button.primary { color: #111; } }
button:focus-visible, a:focus-visible, input:focus-visible, select:focus-visible { outline: 3px solid var(--accent); outline-offset: 2px; }
.feedback { font-weight: 600; } .feedback.correct { color: var(--ok); } .feedback.incorrect, .feedback.invalid { color: var(--bad); }
.choices { list-style: none; padding: 0; } .choices li { margin: 4px 0; }
details { margin: 6px 0; border-left: 3px solid var(--line); padding-left: 10px; }
summary { cursor: pointer; color: var(--accent); }
.diagram svg { max-width: 100%; height: auto; display: block; margin: 8px auto; }
.mjx-chtml { max-width: 100%; } mjx-container[display="true"] { overflow-x: auto; overflow-y: hidden; }
.material { overflow-wrap: anywhere; }
table { border-collapse: collapse; display: block; max-width: 100%; overflow-x: auto; } td, th { border: 1px solid var(--line); padding: 4px 8px; }
.toolbar { display: flex; flex-wrap: wrap; gap: 8px; margin: 8px 0; }
@media print {
  .no-print, .toolbar, .answer-row, footer, header.top { display: none !important; }
  body { background: #fff; color: #000; font-size: 12pt; }
  .q { break-inside: avoid; border-color: #999; }
  details { border: 0; padding: 0; } details > summary { display: none; }
  .print-sol details { display: block; } .print-nosol details { display: none; }
}
main:focus { outline: none; }