:root {
  --bg: #fafaf4;
  --panel: #ffffff;
  --ink: #1a1a1a;
  --muted: #666666;
  --line: #e5e5e0;
  --brand: #a6ce39;        /* Koetai / ORCID green */
  --brand-dark: #8eb22f;
  --accent: #4f6b12;       /* text-safe green for links on light bg */
  --accent-ink: #1a1a1a;
  --code-bg: #f2f2ea;
  --ok: #1e7a46;
  --ok-bg: #e6f4ea;
  --bad: #a33a2b;
  --bad-bg: #fbeae7;
  --warn-bg: #fff6dc;
  --t-wd: #2f6db3;
  --t-sib: #b5462f;
  --t-rp: #7a4fa0;
  --t-py: #3b7d4f;
  --t-ep: #6b6b6b;
  --t-dt: #b07a12;
  --t-rd: #c03a6b;
  --serif: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Ubuntu, sans-serif;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Ubuntu, sans-serif;
  --mono: "JetBrains Mono", ui-monospace, Menlo, monospace;
}
@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --bg: #15181b; --panel: #1c2024; --ink: #e6e8ea; --muted: #9aa4ab; --line: #2e343a;
    --brand: #a6ce39; --brand-dark: #8eb22f; --accent: #b5d95a; --accent-ink: #11140a; --code-bg: #23282d;
    --ok: #6fd39a; --ok-bg: #173323; --bad: #f08f7f; --bad-bg: #3a1f1b; --warn-bg: #3a3218;
    --t-wd: #6fa6e8; --t-sib: #e5866f; --t-rp: #b993dc; --t-py: #7cc48f; --t-ep: #a9a9a9; --t-dt: #e0b04c; --t-rd: #ec82a8;
  }
}
:root[data-theme="dark"] {
  --bg: #15181b; --panel: #1c2024; --ink: #e6e8ea; --muted: #9aa4ab; --line: #2e343a;
  --brand: #a6ce39; --brand-dark: #8eb22f; --accent: #b5d95a; --accent-ink: #11140a; --code-bg: #23282d;
  --ok: #6fd39a; --ok-bg: #173323; --bad: #f08f7f; --bad-bg: #3a1f1b; --warn-bg: #3a3218;
  --t-wd: #6fa6e8; --t-sib: #e5866f; --t-rp: #b993dc; --t-py: #7cc48f; --t-ep: #a9a9a9; --t-dt: #e0b04c; --t-rd: #ec82a8;
}

* { box-sizing: border-box; }
html, body { margin: 0; }
body { background: var(--bg); color: var(--ink); font: 15px/1.6 var(--sans); }
a { color: var(--accent); }
code, pre { font-family: var(--mono); font-size: 0.88em; }
code { background: var(--code-bg); padding: 1px 5px; border-radius: 4px; overflow-wrap: anywhere; }
pre { background: var(--code-bg); padding: 12px 14px; border-radius: 8px; overflow-x: auto; line-height: 1.5; }
pre code { background: none; padding: 0; }
h1, h2, h3 { font-family: var(--serif); font-weight: 600; line-height: 1.25; }
.wrap { max-width: 1080px; margin: 0 auto; padding: 0 16px; }

.top { border-bottom: 1px solid var(--line); background: var(--panel); position: sticky; top: 0; z-index: 5; }
.top-inner { display: flex; align-items: center; gap: 24px; height: 56px; }
.brand { font-family: var(--sans); font-size: 21px; font-weight: 600; letter-spacing: -0.02em; color: var(--ink); text-decoration: none; white-space: nowrap; }
.logo { font-size: 18px; }
.brand .by { font-size: 12px; font-weight: 500; color: var(--muted); margin-left: 4px; letter-spacing: 0; }
.brand .by span { color: var(--ink); }
nav { display: flex; gap: 18px; }
nav a { color: var(--muted); text-decoration: none; font-weight: 500; }
nav a.on { color: var(--ink); box-shadow: inset 0 -2px 0 var(--brand); padding-bottom: 2px; }
.progress { margin-left: auto; color: var(--muted); font-size: 13px; white-space: nowrap; }
@media (max-width: 560px) { .progress, .brand .by { display: none; } .top-inner { gap: 16px; } nav { gap: 12px; } }
.foot { color: var(--muted); font-size: 13px; padding-top: 32px; padding-bottom: 40px; }

/* home */
.hero { padding: 48px 0 24px; max-width: 720px; }
.hero h1 { font-size: 40px; letter-spacing: -0.02em; margin: 0 0 12px; }
.hero p { font-size: 17px; color: var(--muted); }
.btn { display: inline-flex; align-items: center; gap: 6px; border: 1px solid var(--line); background: var(--panel); color: var(--ink); padding: 8px 14px; border-radius: 8px; font: 500 14px var(--sans); cursor: pointer; text-decoration: none; }
.btn:hover { border-color: var(--muted); }
.btn.primary { background: var(--brand); border-color: var(--brand); color: #1a1a1a; }
.btn.primary:hover { background: var(--brand-dark); border-color: var(--brand-dark); }
.btn:disabled { opacity: .55; cursor: progress; }
.tracks { display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr)); gap: 16px; margin: 24px 0; }
.card { background: var(--panel); border: 1px solid var(--line); border-radius: 10px; padding: 18px; transition: border-color .15s; }
.card:hover { border-color: var(--brand); }
.card h3 { margin: 0 0 6px; }
.dot { display: inline-block; width: 10px; height: 10px; border-radius: 50%; margin-right: 6px; vertical-align: 1px; }

/* problem list */
table.list { width: 100%; border-collapse: collapse; background: var(--panel); border: 1px solid var(--line); border-radius: 12px; overflow: hidden; }
.list th, .list td { text-align: left; padding: 9px 12px; border-bottom: 1px solid var(--line); }
.list th { font-size: 12px; text-transform: uppercase; letter-spacing: .04em; color: var(--muted); font-weight: 600; }
.list tr:last-child td { border-bottom: 0; }
.list td.id { font-family: var(--mono); font-weight: 500; }
.list a { text-decoration: none; }
.list .solved { color: var(--ok); font-weight: 600; }
.list .concept { color: var(--muted); }
.table-scroll { overflow-x: auto; }
.filters { display: flex; flex-wrap: wrap; gap: 8px; margin: 0 0 14px; }
.chip { border: 1px solid var(--line); background: var(--panel); border-radius: 999px; padding: 4px 12px; font: 500 13px var(--sans); color: var(--muted); cursor: pointer; }
.chip.on { border-color: var(--ink); color: var(--ink); }

/* tree */
.tree-box { background: var(--panel); border: 1px solid var(--line); border-radius: 12px; padding: 12px; overflow-x: auto; }
.tree-box svg { display: block; margin: 0 auto; max-width: 100%; height: auto; }
.tree-box .edge { fill: none; stroke: var(--muted); stroke-opacity: .45; stroke-width: 1.5; }
.tree-box .node rect { fill: var(--panel); stroke-width: 2; }
.tree-box .node text { font: 600 13px var(--mono); fill: var(--ink); }
.tree-box .node text.sub { font: 400 10px var(--sans); fill: var(--muted); }
.tree-box .node.solved text { fill: #fff; }
.tree-box .node.solved text.sub { fill: rgba(255,255,255,.85); }
.tree-box .node:hover rect { stroke-width: 3.5; }
.tree-box a { cursor: pointer; }
.legend { display: flex; gap: 16px; flex-wrap: wrap; color: var(--muted); font-size: 13px; margin: 10px 0 0; }

/* problem page */
.crumbs { color: var(--muted); font-size: 13px; margin: 24px 0 4px; }
.ptitle { display: flex; align-items: baseline; gap: 12px; flex-wrap: wrap; margin: 0 0 6px; }
.ptitle h1 { margin: 0; font-size: 30px; }
.ptitle .pid { font-family: var(--mono); color: var(--muted); font-size: 18px; }
.meta { display: flex; flex-wrap: wrap; gap: 8px 16px; color: var(--muted); font-size: 13px; margin-bottom: 18px; align-items: center; }
.badge { display: inline-flex; align-items: center; border-radius: 999px; padding: 2px 10px; font-size: 12px; font-weight: 600; color: #fff; }
.solved-badge { background: var(--ok-bg); color: var(--ok); }
.cols { display: grid; grid-template-columns: minmax(0, 1fr) minmax(0, 1fr); gap: 28px; align-items: start; }
@media (max-width: 900px) { .cols { grid-template-columns: minmax(0, 1fr); } }
.section h2 { font-size: 19px; margin: 18px 0 6px; }
.section:first-child h2 { margin-top: 0; }
.task { background: var(--panel); border: 1px solid var(--line); border-left: 4px solid var(--brand); border-radius: 8px; padding: 12px 16px; }
.task .ret { margin-top: 8px; font-size: 14px; color: var(--muted); }
details { margin-top: 12px; }
summary { cursor: pointer; color: var(--accent); font-weight: 500; }
.note { background: var(--warn-bg); border-radius: 8px; padding: 10px 14px; font-size: 14px; margin-bottom: 16px; }

.editor-pane { position: sticky; top: 72px; }
@media (max-width: 900px) { .editor-pane { position: static; } }
.endpoint { font-size: 13px; color: var(--muted); margin-bottom: 6px; display: flex; justify-content: space-between; gap: 8px; flex-wrap: wrap; }
.CodeMirror { height: 320px; border: 1px solid var(--line); border-radius: 8px; font: 13px/1.5 var(--mono); background: var(--panel); color: var(--ink); }
.CodeMirror-gutters { background: var(--code-bg); border-right: 1px solid var(--line); }
.CodeMirror-linenumber { color: var(--muted); }
.CodeMirror-cursor { border-left-color: var(--ink); }
.CodeMirror-selected { background: var(--code-bg) !important; }
.cm-s-default .cm-keyword { color: #b03a84; font-weight: 500; }
.cm-s-default .cm-variable-2 { color: var(--t-wd); }
.cm-s-default .cm-atom { color: var(--accent); }
.cm-s-default .cm-string { color: #b0702f; }
.cm-s-default .cm-comment { color: var(--muted); font-style: italic; }
.cm-s-default .cm-builtin, .cm-s-default .cm-variable-3, .cm-s-default .cm-meta { color: var(--t-rp); }
.cm-s-default .cm-bracket { color: var(--muted); }
.actions { display: flex; gap: 8px; flex-wrap: wrap; margin: 10px 0; align-items: center; }
.actions .spacer { flex: 1; }
.kbd { font-size: 12px; color: var(--muted); }
.verdict { border-radius: 8px; padding: 12px 14px; margin: 10px 0; font-size: 14px; overflow-wrap: anywhere; }
.verdict.ok { background: var(--ok-bg); color: var(--ok); }
.verdict.bad { background: var(--bad-bg); color: var(--bad); }
.verdict.info { background: var(--code-bg); color: var(--muted); }
.verdict ul { margin: 6px 0 0; padding-left: 18px; }
.verdict code { background: transparent; }
.results { max-height: 380px; overflow: auto; border: 1px solid var(--line); border-radius: 8px; background: var(--panel); }
.results table { border-collapse: collapse; width: 100%; font: 12.5px var(--mono); }
.results th, .results td { padding: 5px 9px; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
.results th { position: sticky; top: 0; background: var(--code-bg); font-weight: 500; }
.results td a { text-decoration: none; }
.results .count { font: 12px var(--sans); color: var(--muted); padding: 6px 9px; }
.next { margin-top: 18px; display: flex; gap: 8px; flex-wrap: wrap; align-items: center; }
.reveal { border-top: 1px dashed var(--line); margin-top: 18px; padding-top: 6px; }
.about { max-width: 760px; }
.about h2 { margin-top: 28px; }
.empty { color: var(--muted); }

/* guides, answers, local endpoint */
.step { font-size: 12px; text-transform: uppercase; letter-spacing: .05em; color: var(--muted); margin-bottom: 2px; }
.section h3 { font-size: 15px; margin: 16px 0 4px; font-family: var(--sans); }
table.mini { border-collapse: collapse; width: 100%; font-size: 13.5px; margin: 8px 0; display: block; overflow-x: auto; }
table.mini th, table.mini td { border-bottom: 1px solid var(--line); padding: 6px 8px; text-align: left; vertical-align: top; }
table.mini th { font-size: 12px; color: var(--muted); font-weight: 600; }
.done-card label, .connect label { display: block; font-weight: 500; font-size: 14px; margin-bottom: 4px; }
.done-card input, .connect input { flex: 1; min-width: 0; padding: 8px 10px; border: 1px solid var(--line); border-radius: 8px; background: var(--panel); color: var(--ink); font: 14px var(--mono); }
.done-card .actions, .connect .actions { flex-wrap: nowrap; }
.tree-box .edge.any { stroke-dasharray: 4 4; }
.section details { margin-top: 8px; }