:root {
  --bg: #fafaf7; --card: #ffffff; --ink: #1b1f27; --muted: #5d6573; --line: #e3e3dc;
  --accent: #2557d6; --accent-ink: #ffffff; --good: #1d8a4c; --bad: #c0392b; --warn: #b7791f;
  --soft: #eef2fd;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #14171c; --card: #1c2027; --ink: #e8eaee; --muted: #9aa3b2; --line: #2b313b;
    --accent: #6c93ff; --accent-ink: #0d1117; --good: #4cc786; --bad: #ff7b6b; --warn: #e2b04a;
    --soft: #1f2a44;
  }
}
:root[data-theme="dark"] {
  --bg: #14171c; --card: #1c2027; --ink: #e8eaee; --muted: #9aa3b2; --line: #2b313b;
  --accent: #6c93ff; --accent-ink: #0d1117; --good: #4cc786; --bad: #ff7b6b; --warn: #e2b04a;
  --soft: #1f2a44;
}
* { box-sizing: border-box; }
body { margin: 0; background: var(--bg); color: var(--ink);
  font: 17px/1.55 system-ui, -apple-system, "Segoe UI", Roboto, sans-serif; }
a { color: var(--accent); }
.top { display: flex; align-items: center; justify-content: space-between; flex-wrap: wrap; gap: 8px;
  padding: 12px 16px; border-bottom: 1px solid var(--line); background: var(--card); position: sticky; top: 0; z-index: 5; }
.brand { font-weight: 700; font-size: 1.15rem; text-decoration: none; color: var(--ink); }
.top nav a { margin-left: 16px; text-decoration: none; color: var(--muted); }
.top nav a:hover { color: var(--accent); }
main { max-width: 860px; margin: 0 auto; padding: 24px 16px 48px; }
footer { max-width: 860px; margin: 0 auto; padding: 16px; color: var(--muted); font-size: .85rem; border-top: 1px solid var(--line); }
h1 { font-size: 1.8rem; margin: .2em 0 .4em; }
h2 { font-size: 1.25rem; margin: 1.4em 0 .5em; }
.sub { color: var(--muted); margin-top: 0; }
.grid { display: grid; gap: 12px; grid-template-columns: repeat(auto-fill, minmax(240px, 1fr)); }
.card { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 16px; }
a.card { text-decoration: none; color: inherit; display: block; }
a.card:hover { border-color: var(--accent); }
.card h3 { margin: 0 0 4px; font-size: 1.1rem; }
.card p { margin: 0; color: var(--muted); font-size: .92rem; }
.bar { height: 8px; background: var(--line); border-radius: 4px; overflow: hidden; margin-top: 10px; }
.bar > i { display: block; height: 100%; background: var(--accent); }
.btn { display: inline-block; border: 1px solid var(--accent); background: var(--accent); color: var(--accent-ink);
  padding: 8px 16px; border-radius: 8px; font: inherit; cursor: pointer; text-decoration: none; }
.btn.ghost { background: transparent; color: var(--accent); }
.btn.small { padding: 4px 10px; font-size: .9rem; }
.btn:disabled { opacity: .5; cursor: default; }
.row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; }
.pill { display: inline-block; padding: 1px 9px; border-radius: 99px; background: var(--soft); color: var(--accent); font-size: .78rem; margin-right: 4px; }
.problem { background: var(--card); border: 1px solid var(--line); border-radius: 12px; padding: 20px; margin: 12px 0; font-size: 1.05rem; }
.choices { display: grid; gap: 8px; margin: 14px 0; }
.choice { text-align: left; border: 1px solid var(--line); background: var(--card); color: var(--ink);
  padding: 10px 14px; border-radius: 8px; font: inherit; cursor: pointer; }
.choice:hover { border-color: var(--accent); }
.choice.sel { border-color: var(--accent); background: var(--soft); }
.choice.right { border-color: var(--good); background: color-mix(in srgb, var(--good) 15%, transparent); }
.choice.wrong { border-color: var(--bad); background: color-mix(in srgb, var(--bad) 15%, transparent); }
input[type=number], input[type=text] { font: inherit; padding: 8px 12px; border-radius: 8px; border: 1px solid var(--line);
  background: var(--card); color: var(--ink); width: 9em; }
.hint { border-left: 4px solid var(--warn); background: color-mix(in srgb, var(--warn) 10%, transparent); padding: 8px 14px; margin: 8px 0; border-radius: 0 8px 8px 0; }
.solution { border-left: 4px solid var(--accent); background: var(--soft); padding: 10px 16px; margin: 12px 0; border-radius: 0 8px 8px 0; }
.msg-good { color: var(--good); font-weight: 600; }
.msg-bad { color: var(--bad); font-weight: 600; }
.list a { display: flex; justify-content: space-between; gap: 8px; padding: 10px 14px; text-decoration: none; color: var(--ink);
  border: 1px solid var(--line); background: var(--card); border-radius: 8px; margin-bottom: 6px; }
.list a:hover { border-color: var(--accent); }
.done { color: var(--good); font-weight: 700; }
.timer { font: 700 1.3rem ui-monospace, Menlo, Consolas, monospace; }
.timer.low { color: var(--bad); }
.qnav { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0; }
.qnav button { width: 38px; height: 34px; border: 1px solid var(--line); background: var(--card); color: var(--ink); border-radius: 6px; cursor: pointer; font: inherit; }
.qnav button.cur { border-color: var(--accent); outline: 2px solid var(--accent); }
.qnav button.ans { background: var(--soft); }
table.t { border-collapse: collapse; width: 100%; background: var(--card); }
table.t th, table.t td { border: 1px solid var(--line); padding: 8px 10px; text-align: left; }
.note { background: var(--soft); border-radius: 8px; padding: 10px 14px; font-size: .92rem; }
.crumbs { font-size: .9rem; color: var(--muted); margin-bottom: 6px; }
@media (max-width: 520px) { body { font-size: 16px; } h1 { font-size: 1.5rem; } }
.cells { display: grid; grid-template-columns: repeat(auto-fill, minmax(38px, 1fr)); gap: 6px; margin: 14px 0; }
.cell { display: flex; align-items: center; justify-content: center; height: 34px; border: 1px solid var(--line); border-radius: 6px;
  background: var(--card); color: var(--ink); text-decoration: none; font-size: .85rem; }
.cell:hover { border-color: var(--accent); }
.cell.done { background: color-mix(in srgb, var(--good) 22%, transparent); border-color: var(--good); }
.cell.cur { outline: 2px solid var(--accent); }
select { font: inherit; padding: 6px 8px; border-radius: 8px; border: 1px solid var(--line); background: var(--card); color: var(--ink); }
code { background: var(--soft); padding: 1px 6px; border-radius: 4px; }

:focus-visible { outline: 3px solid #f5a623; outline-offset: 2px; }
@media (prefers-reduced-motion: reduce) { * { transition: none !important; animation: none !important; } }

.top nav button.theme { margin-left: 16px; background: none; border: 1px solid var(--line); color: var(--muted); border-radius: 8px; padding: 2px 8px; cursor: pointer; font: inherit; }
.ws li { margin: 0 0 14px; } .wsgap { height: 70px; } .ws.key { columns: 2; } .pagebreak { break-after: page; }
@media print {
  .top, footer, .noprint { display: none !important; }
  body { background: #fff; color: #000; font-size: 12pt; } .wsgap { height: 90px; } .ws li { break-inside: avoid; }
  .pagebreak { height: 0; }
}

.stack { display: flex; flex-direction: column; gap: 10px; max-width: 460px; }
input[type=email], input[type=password], textarea { font: inherit; padding: 8px 12px; border-radius: 8px; border: 1px solid var(--line); background: var(--card); color: var(--ink); width: 100%; }
textarea { max-width: 640px; resize: vertical; }
input[type=checkbox] { width: 1.1em; height: 1.1em; }
.post .problem { overflow-wrap: anywhere; }
@media print { .post { break-inside: avoid; } }

.skip { position: absolute; left: -999px; top: 0; background: var(--accent); color: var(--accent-ink); padding: 8px 14px; z-index: 20; border-radius: 0 0 8px 0; }
.skip:focus { left: 0; }
.srch { list-style: none; padding: 0; margin: 0; } .srch li { padding: 8px 0; border-bottom: 1px solid var(--line); }
input[type=search] { font: inherit; padding: 8px 12px; border-radius: 8px; border: 1px solid var(--line); background: var(--card); color: var(--ink); }
main:focus, h1:focus { outline: none; }
@media (max-width: 520px) {
  .top { padding: 8px 12px; } .top nav { display: flex; flex-wrap: wrap; gap: 2px 12px; } .top nav a, .top nav button.theme { margin-left: 0; font-size: .95rem; }
  .brand { font-size: 1rem; }
}