/* Problem Set — shared styles (light + dark), same palette as the study books */
:root {
  --bg: #fbfaf7; --bg-soft: #f2f0ea; --panel: #ffffff; --text: #1f2328; --muted: #5d636b;
  --border: #e1ddd3; --accent: #2f5fa7; --accent-soft: #e6eefa;
  --code-bg: #f5f3ee; --code-head: #ebe7de;
  --easy: #2e8b57; --medium: #b07d00; --hard: #c0392b; --oop: #7b4bb7;
  --good-bg: #e9f6ec; --good-bd: #2e8b57; --bad-bg: #fdeaea; --bad-bd: #c0392b;
  --note-bg: #e8f0fb; --note-bd: #2f5fa7; --pit-bg: #fff4dd; --pit-bd: #c98a00;
  --shadow: 0 1px 3px rgba(0,0,0,.06), 0 4px 14px rgba(0,0,0,.04);
  --radius: 10px;
  --mono: ui-monospace, SFMono-Regular, Menlo, Consolas, "Liberation Mono", monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color-scheme: light;
}
@media (prefers-color-scheme: dark) {
  /* no theme chosen yet (scripts off): follow the OS */
  :root:not([data-theme]) {
    --bg: #15171b; --bg-soft: #1c1f24; --panel: #1d2026; --text: #e6e6e3; --muted: #a3a8b0;
    --border: #30343c; --accent: #7fb0ff; --accent-soft: #1f2b40;
    --code-bg: #101215; --code-head: #1a1d22;
    --easy: #4fbf7f; --medium: #e5b53b; --hard: #ff7b72; --oop: #c39bff;
    --good-bg: #15291d; --good-bd: #4fbf7f; --bad-bg: #331a1a; --bad-bd: #ff7b72;
    --note-bg: #172235; --note-bd: #7fb0ff; --pit-bg: #2d2511; --pit-bd: #e5b53b;
    --shadow: 0 1px 3px rgba(0,0,0,.4);
    color-scheme: dark;
  }
}
/* the theme chosen in the site header (shared/site.js) */
:root[data-theme="dark"] {
  --bg: #15171b; --bg-soft: #1c1f24; --panel: #1d2026; --text: #e6e6e3; --muted: #a3a8b0;
  --border: #30343c; --accent: #7fb0ff; --accent-soft: #1f2b40;
  --code-bg: #101215; --code-head: #1a1d22;
  --easy: #4fbf7f; --medium: #e5b53b; --hard: #ff7b72; --oop: #c39bff;
  --good-bg: #15291d; --good-bd: #4fbf7f; --bad-bg: #331a1a; --bad-bd: #ff7b72;
  --note-bg: #172235; --note-bd: #7fb0ff; --pit-bg: #2d2511; --pit-bd: #e5b53b;
  --shadow: 0 1px 3px rgba(0,0,0,.4);
  color-scheme: dark;
}
* { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; }
body { margin: 0; background: var(--bg); color: var(--text); font: 16px/1.65 var(--sans); }
a { color: var(--accent); }
main { max-width: 980px; margin: 0 auto; padding: 18px 16px 70px; }
h1 { font-size: 2rem; line-height: 1.2; margin: .3em 0 .25em; }
h2 { font-size: 1.3rem; margin: 1.8em 0 .5em; }
h3 { font-size: 1.05rem; margin: 1.3em 0 .4em; }
code, pre, kbd, textarea { font-family: var(--mono); }
code { font-size: .9em; background: var(--code-bg); border: 1px solid var(--border); border-radius: 5px; padding: 0 4px; }
pre code { background: none; border: 0; padding: 0; font-size: inherit; }
kbd { font-size: 12px; border: 1px solid var(--border); border-bottom-width: 2px; border-radius: 5px; padding: 0 5px; background: var(--bg-soft); }
.muted { color: var(--muted); }

/* top bar */
.topbar { display: flex; flex-wrap: wrap; gap: 6px 16px; align-items: center; padding: 10px 16px; border-bottom: 1px solid var(--border); background: var(--panel); font-size: .93rem; }
.topbar a { text-decoration: none; }
.topbar .brand { font-weight: 700; color: var(--text); }
.topbar .spacer { flex: 1; }
.eyebrow { text-transform: uppercase; letter-spacing: .08em; font-size: 12.5px; font-weight: 700; color: var(--accent); }
.lead { color: var(--muted); font-size: 1.08rem; margin: 0 0 18px; }

/* badges */
.badge { display: inline-block; font: 700 11.5px/1.7 var(--sans); text-transform: uppercase; letter-spacing: .05em; padding: 0 8px; border-radius: 99px; border: 1.5px solid currentColor; white-space: nowrap; }
.badge.easy { color: var(--easy); } .badge.medium { color: var(--medium); } .badge.hard { color: var(--hard); } .badge.oop { color: var(--oop); }
.tag { display: inline-block; font-size: 12px; border: 1px solid var(--border); border-radius: 99px; padding: 0 9px; color: var(--muted); background: var(--bg-soft); white-space: nowrap; }

/* buttons and inputs */
.btn { display: inline-flex; align-items: center; gap: 6px; text-decoration: none; font: 600 14px var(--sans); padding: 7px 14px; border-radius: 8px;
  border: 1px solid var(--border); background: var(--panel); color: var(--text); cursor: pointer; }
.btn:hover { border-color: var(--accent); }
.btn.primary { background: var(--accent); border-color: var(--accent); color: var(--bg); }
.btn.small { font-size: 12.5px; padding: 3px 10px; }
.btn:disabled { opacity: .45; cursor: default; }
input[type=search], select, textarea { font: inherit; color: var(--text); background: var(--panel); border: 1px solid var(--border); border-radius: 8px; padding: 7px 10px; max-width: 100%; }
textarea { width: 100%; min-height: 150px; font-size: 13.5px; line-height: 1.5; resize: vertical; }
input:focus-visible, select:focus-visible, textarea:focus-visible, .btn:focus-visible, .chip:focus-visible { outline: 2px solid var(--accent); outline-offset: 1px; }

/* index: progress + filters + list */
.cards { display: grid; grid-template-columns: repeat(auto-fit, minmax(190px, 1fr)); gap: 12px; margin: 14px 0 6px; }
.stat { background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius); padding: 12px 14px; box-shadow: var(--shadow); }
.stat .label { font-size: 13px; font-weight: 700; text-transform: uppercase; letter-spacing: .05em; }
.stat .num { font-size: 1.5rem; font-weight: 700; }
.bar { height: 7px; background: var(--bg-soft); border-radius: 99px; overflow: hidden; border: 1px solid var(--border); }
.bar > span { display: block; height: 100%; background: currentColor; width: 0; transition: width .3s; }
.steps { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 12px; padding: 0; list-style: none; counter-reset: s; }
.steps li { background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius); padding: 12px 14px 12px 46px; position: relative; counter-increment: s; }
.steps li::before { content: counter(s); position: absolute; left: 14px; top: 13px; width: 22px; height: 22px; border-radius: 50%; background: var(--accent); color: var(--bg); font-size: 12px; font-weight: 700; display: grid; place-items: center; }
.filters { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 18px 0 12px; }
.chip { font: 600 13.5px var(--sans); padding: 5px 13px; border-radius: 99px; cursor: pointer; border: 1.5px solid var(--border); background: var(--panel); color: var(--text); }
.chip[aria-pressed="true"] { background: var(--accent); border-color: var(--accent); color: var(--bg); }
.filters input[type=search] { flex: 1 1 200px; }
.filters label { font-size: 14px; display: inline-flex; gap: 6px; align-items: center; }
.plist { list-style: none; padding: 0; margin: 0; border: 1px solid var(--border); border-radius: var(--radius); background: var(--panel); box-shadow: var(--shadow); overflow: hidden; }
.plist li + li { border-top: 1px solid var(--border); }
.plist a { display: grid; grid-template-columns: 26px 52px 1fr auto; gap: 4px 12px; align-items: center; padding: 10px 14px; color: inherit; text-decoration: none; }
.plist a:hover { background: var(--accent-soft); }
.plist .pid { font: 600 13px var(--mono); color: var(--muted); }
.plist .ptitle { font-weight: 600; min-width: 0; }
.plist .ptags { grid-column: 3 / 4; display: flex; flex-wrap: wrap; gap: 4px; }
.plist .pbadge { grid-row: 1 / 3; grid-column: 4; }
.plist .status { grid-row: 1 / 3; font-size: 17px; text-align: center; }
.status.solved { color: var(--easy); }
.status.tried { color: var(--medium); }
.empty { padding: 22px; text-align: center; color: var(--muted); }
@media (max-width: 560px) {
  .plist a { grid-template-columns: 22px 1fr auto; padding: 10px 12px; }
  .plist .pid { grid-column: 2; }
  .plist .ptitle, .plist .ptags { grid-column: 2 / 4; }
  .plist .pbadge { grid-row: 1; grid-column: 3; }
  .plist .status { grid-row: 1 / 4; }
}

/* problem page */
.crumbs { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; justify-content: space-between; font-size: .93rem; }
.crumbs .nav { display: flex; gap: 6px; }
.phead { display: flex; flex-wrap: wrap; align-items: center; gap: 8px 12px; }
.phead h1 { margin-bottom: 0; }
.meta { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0 4px; }
.section { background: var(--panel); border: 1px solid var(--border); border-radius: var(--radius); padding: 4px 18px 14px; margin: 16px 0; box-shadow: var(--shadow); }
.section > h2:first-child { margin-top: .7em; }
.box { border-left: 4px solid var(--note-bd); background: var(--note-bg); border-radius: 8px; padding: 10px 14px; margin: 12px 0; }
.box.oop { border-color: var(--oop); background: var(--bg-soft); }
.box.warn { border-color: var(--pit-bd); background: var(--pit-bg); }
.box > :first-child { margin-top: 0; } .box > :last-child { margin-bottom: 0; }
.io { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin: 10px 0 4px; }
@media (max-width: 640px) { .io { grid-template-columns: 1fr; } }
.pane { border: 1px solid var(--border); border-radius: 8px; overflow: hidden; min-width: 0; background: var(--code-bg); }
.pane .head { display: flex; align-items: center; justify-content: space-between; gap: 8px; padding: 3px 6px 3px 12px; background: var(--code-head); font-size: 12.5px; font-weight: 700; color: var(--muted); text-transform: uppercase; letter-spacing: .05em; }
.pane pre { margin: 0; padding: 10px 12px; font-size: 13.5px; line-height: 1.5; overflow: auto; max-height: 360px; }
.explain { font-size: .95rem; color: var(--muted); margin: 4px 0 18px; }
details.hint { border: 1px solid var(--border); border-radius: 8px; padding: 6px 12px; margin: 8px 0; background: var(--bg-soft); }
details.hint summary { cursor: pointer; font-weight: 600; }
ul.tight { margin: .3em 0; padding-left: 1.3em; }

/* tests + checker */
.tests { display: flex; flex-wrap: wrap; gap: 6px; margin: 8px 0 12px; }
.tbtn { font: 600 13px var(--sans); padding: 4px 11px; border-radius: 99px; cursor: pointer; border: 1.5px solid var(--border); background: var(--panel); color: var(--text); }
.tbtn[aria-pressed="true"] { border-color: var(--accent); background: var(--accent-soft); }
.tbtn.pass { border-color: var(--good-bd); } .tbtn.pass::before { content: "✓ "; color: var(--good-bd); }
.tbtn.fail::before { content: "✗ "; color: var(--bad-bd); }
.result { border-radius: 8px; padding: 10px 14px; margin: 10px 0; border-left: 4px solid; }
.result.ok { background: var(--good-bg); border-color: var(--good-bd); }
.result.bad { background: var(--bad-bg); border-color: var(--bad-bd); }
.result pre { margin: 6px 0 0; white-space: pre-wrap; word-break: break-all; font-size: 13px; }
.row { display: flex; flex-wrap: wrap; gap: 8px; align-items: center; margin: 10px 0; }
.cmd { display: flex; gap: 8px; align-items: stretch; margin: 8px 0; }
.cmd pre { flex: 1; margin: 0; padding: 8px 12px; background: var(--code-bg); border: 1px solid var(--border); border-radius: 8px; overflow: auto; font-size: 13.5px; }
.solvedflag { font-weight: 700; color: var(--easy); }

/* guide page */
.tabs { display: flex; flex-wrap: wrap; gap: 6px; margin: 10px 0 0; }
.codeblock { border: 1px solid var(--border); border-radius: 8px; overflow: hidden; background: var(--code-bg); margin: 10px 0 16px; }
.codeblock .head { display: flex; justify-content: space-between; align-items: center; padding: 3px 6px 3px 12px; background: var(--code-head); font: 600 12.5px var(--mono); color: var(--muted); }
.codeblock pre { margin: 0; padding: 12px 14px; overflow: auto; font-size: 13.5px; line-height: 1.55; }
table { border-collapse: collapse; width: 100%; font-size: .94rem; }
.tablewrap { overflow-x: auto; }
th, td { text-align: left; border-bottom: 1px solid var(--border); padding: 6px 10px; vertical-align: top; }
th { background: var(--bg-soft); }
footer { margin-top: 40px; color: var(--muted); font-size: .9rem; }
@media (max-width: 560px) {
  h1 { font-size: 1.6rem; }
  .section { padding: 2px 13px 12px; }
  main { padding-top: 12px; }
}