:root {
  --bg: #fafaf9; --fg: #1c1917; --muted: #78716c; --card: #fff; --line: #d6d3d1;
  --accent: #1d4ed8; --ok: #15803d; --bad: #b91c1c;
  --c1: #1d4ed8; --c2: #c2410c; --c3: #15803d; --c4: #7e22ce;
}
@media (prefers-color-scheme: dark) {
  :root {
    --bg: #1c1917; --fg: #f5f5f4; --muted: #a8a29e; --card: #292524; --line: #44403c;
    --accent: #60a5fa; --ok: #4ade80; --bad: #f87171;
    --c1: #60a5fa; --c2: #fb923c; --c3: #4ade80; --c4: #c084fc;
  }
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--fg); font: 16px/1.5 system-ui, sans-serif; }
main { max-width: 760px; margin: 0 auto; padding: 16px; }
h1 { margin: 0; font-size: 1.5rem; }
.sub { color: var(--muted); margin-top: 4px; }
form { display: grid; grid-template-columns: repeat(auto-fit, minmax(200px, 1fr)); gap: 12px; margin: 16px 0; }
label { display: flex; flex-direction: column; gap: 4px; font-size: .875rem; color: var(--muted); }
label.wide { grid-column: 1 / -1; }
select, input { font: inherit; padding: 8px; border: 1px solid var(--line); border-radius: 6px; background: var(--card); color: var(--fg); }
.actions { grid-column: 1 / -1; display: flex; gap: 8px; }
.actions button { padding: 10px 16px; font: inherit; font-weight: 600; border-radius: 6px; cursor: pointer; border: 1px solid var(--line); background: var(--card); color: var(--fg); }
#go { flex: 1; border: 0; background: var(--accent); color: #fff; }
.actions button:disabled { opacity: .6; cursor: wait; }
.badge { display: inline-block; margin: 0 6px 0 0; padding: 0 6px; border: 1px solid var(--line); border-radius: 10px; }
.badge.ok { color: var(--ok); border-color: var(--ok); }
.skeleton { color: var(--muted); animation: pulse 1.4s ease-in-out infinite; }
.skeleton .bar { height: 12px; border-radius: 4px; background: var(--line); margin: 10px 0; }
.card.fail { border-color: var(--bad); color: var(--bad); }
@keyframes pulse { 50% { opacity: .45; } }
@media (prefers-reduced-motion: reduce) { .skeleton { animation: none; } }
#status { color: var(--muted); min-height: 1.5em; }
#status.error { color: var(--bad); }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 8px; padding: 16px; margin-bottom: 16px; }
.card h3 { margin: 0 0 4px; font-size: 1.05rem; }
.tag { margin: 0 0 8px; font-size: .75rem; color: var(--muted); }
.choices { list-style: none; padding: 0; margin: 12px 0 0; display: grid; gap: 8px; }
.choices button { width: 100%; text-align: left; padding: 10px; font: inherit; color: var(--fg); background: transparent; border: 1px solid var(--line); border-radius: 6px; cursor: pointer; }
.choices button:hover:not(:disabled) { border-color: var(--accent); }
.choices button:disabled { cursor: default; }
.choices .right { border-color: var(--ok); box-shadow: inset 0 0 0 1px var(--ok); }
.choices .wrong { border-color: var(--bad); box-shadow: inset 0 0 0 1px var(--bad); }
.explain { margin: 12px 0 0; padding-top: 12px; border-top: 1px solid var(--line); }
figure { margin: 8px 0; text-align: center; }
.graphic { width: 100%; max-width: 480px; height: auto; }
.g-title { font-size: 13px; font-weight: 600; fill: var(--fg); }
.g-label { font-size: 11px; fill: var(--fg); }
.g-tick { font-size: 10px; fill: var(--muted); }
.g-grid { stroke: var(--line); stroke-width: 1; }
.g-axis { stroke: var(--muted); stroke-width: 1; }
.g-axis3 { stroke: var(--fg); stroke-width: 1.5; }
.g-surf { stroke: var(--c1); stroke-width: 1; }
.g-error { color: var(--muted); font-style: italic; }
.rot { width: 60%; padding: 0; }
.step { margin: 0; }

nav { display: flex; flex-wrap: wrap; gap: 4px; margin: 12px 0; border-bottom: 1px solid var(--line); }
nav a { padding: 8px 12px; color: var(--muted); text-decoration: none; border-bottom: 2px solid transparent; }
nav a.on { color: var(--fg); border-color: var(--accent); }
fieldset { border: 1px solid var(--line); border-radius: 6px; margin: 0; display: grid; gap: 6px; }
fieldset.wide { grid-column: 1 / -1; }
legend { font-size: .875rem; color: var(--muted); }
label.check { flex-direction: row; align-items: baseline; gap: 6px; color: var(--fg); font-size: 1rem; }
label.check small { color: var(--muted); }
#exam_info { color: var(--muted); }
#exam_info.error, .error { color: var(--bad); }
.btn { display: inline-block; padding: 8px 12px; font: inherit; color: var(--fg); background: var(--card); border: 1px solid var(--line); border-radius: 6px; cursor: pointer; text-decoration: none; }
.btn.primary { background: var(--accent); border-color: var(--accent); color: #fff; font-weight: 600; }
.btn.small { margin-top: 12px; font-size: .8rem; padding: 4px 8px; }
.row { display: flex; gap: 8px; align-items: center; }
.row > div { flex: 1; }
.row h3 { margin: 0; }
.row .tag { margin: 0; }
.sec { margin: 24px 0 12px; }
progress { width: 100%; height: 14px; }
.choices .picked { border-color: var(--accent); box-shadow: inset 0 0 0 2px var(--accent); }
.bar-sticky { position: sticky; bottom: 0; display: flex; justify-content: space-between; align-items: center; gap: 12px; padding: 12px 0; background: var(--bg); border-top: 1px solid var(--line); }
.result.pass { border-color: var(--ok); }
.result.fail { border-color: var(--bad); }
.result h3 { margin-bottom: 8px; }
.result p { margin: 4px 0; }
.wide { grid-column: 1 / -1; }