:root {
  --bg: #eef3f8;
  --ink: #1a2332;
  --muted: #5a6a7e;
  --dim: #7b8898;
  --line: #c5d2e0;
  --accent: #2b5ea7;
  --accent-dim: #1e447c;
  --paper: #f7fafc;
  --ok: #1f6b4a;
  --bad: #a33a32;
  --sans: "PingFang SC", "Hiragino Sans GB", "Noto Sans SC", ui-sans-serif, system-ui, sans-serif;
  --serif: "Songti SC", "STSong", "Noto Serif CJK SC", Georgia, serif;
  --mono: "SFMono-Regular", ui-monospace, Menlo, Consolas, monospace;
  --page: min(42rem, calc(100vw - 2.5rem));
}
* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background-color: var(--bg);
  background-image:
    linear-gradient(rgba(43, 94, 167, 0.07) 1px, transparent 1px),
    linear-gradient(90deg, rgba(43, 94, 167, 0.07) 1px, transparent 1px);
  background-size: 28px 28px;
  background-attachment: fixed;
  font: 16px/1.75 var(--sans);
}
a { color: var(--accent); text-underline-offset: 0.18em; }
a:focus-visible, button:focus-visible, input:focus-visible, textarea:focus-visible {
  outline: 2px solid var(--accent); outline-offset: 3px;
}
button, input, textarea, select { font: inherit; color: inherit; }
code { font-family: var(--mono); font-size: 0.92em; }
.skip {
  position: absolute; left: 12px; top: 12px; z-index: 20;
  padding: 8px 12px; background: var(--accent); color: #fff;
  transform: translateY(-160%);
}
.skip:focus { transform: none; }
.top {
  position: sticky; top: 0; z-index: 10;
  display: flex; align-items: center; justify-content: space-between; gap: 12px;
  padding: 10px 4vw;
  background: color-mix(in srgb, var(--bg) 88%, white);
  border-bottom: 1px solid var(--line);
  backdrop-filter: blur(12px);
}
.top a { color: var(--muted); text-decoration: none; font: 700 12px/1 var(--mono); letter-spacing: 0.08em; }
.top a:hover { color: var(--ink); }
.top strong { font: 700 14px/1 var(--serif); color: var(--ink); }
.rail {
  width: var(--page); margin: 0.8rem auto 0;
  display: flex; flex-wrap: wrap; gap: 8px 14px;
  font: 700 11px/1 var(--mono); letter-spacing: 0.06em;
}
.rail a { color: var(--dim); text-decoration: none; }
.rail a[aria-current] { color: var(--accent); }
main { width: var(--page); margin: 0 auto; padding: 2.6rem 0 4.5rem; }
.kicker { margin: 0 0 12px; color: var(--accent); font: 700 11px/1.4 var(--mono); letter-spacing: 0.12em; }
h1 { margin: 0 0 16px; font: 700 clamp(28px, 6vw, 44px)/1.2 var(--serif); letter-spacing: -0.03em; }
h2 { margin: 2.2rem 0 12px; font: 700 22px/1.3 var(--serif); }
p, li { color: var(--muted); }
p.lead { color: var(--ink); font-size: 17px; }
.path { list-style: none; padding: 0; margin: 2rem 0; }
.path li { border-top: 1px solid var(--line); padding: 14px 0; display: grid; grid-template-columns: 4.5rem 1fr; gap: 12px; }
.path time { color: var(--accent); font: 700 12px/1.6 var(--mono); }
.path a { color: var(--ink); font-weight: 700; text-decoration: none; }
.path a:hover { color: var(--accent); }
.path small { display: block; color: var(--muted); font-weight: 400; margin-top: 4px; }
.work {
  margin: 1.6rem 0 2rem; padding: 1.15rem 1.2rem 1.3rem;
  background: #fff; border: 1px solid var(--accent);
}
.work h2 { margin-top: 0; }
.work label { display: grid; gap: 6px; margin: 10px 0; color: var(--ink); }
.work input, .work select, .work textarea {
  padding: 8px 10px; border: 1px solid var(--line); background: #fff;
}
.act { min-height: 40px; padding: 0 14px; cursor: pointer; }
.choices { display: grid; gap: 8px; margin: 16px 0; }
.choices button, .act {
  text-align: left; min-height: 46px; padding: 10px 14px;
  border: 1px solid var(--line); background: #fff; color: var(--ink); cursor: pointer;
}
.choices button:hover, .act:hover { border-color: var(--accent); color: var(--accent); }
.choices button.is-ok { border-color: var(--ok); color: var(--ok); }
.choices button.is-bad { border-color: var(--bad); color: var(--bad); }
.act { background: var(--accent); color: #fff; border-color: var(--accent); }
.act:hover { color: #fff; filter: brightness(1.05); }
.out {
  margin: 12px 0 0; padding: 12px 14px; background: var(--paper);
  border-left: 3px solid var(--accent); color: var(--ink);
}
.out.is-ok { border-color: var(--ok); }
.out.is-bad { border-color: var(--bad); }
pre {
  overflow: auto; padding: 14px 16px; background: #1a2332;
  border: 1px solid var(--line); font: 13px/1.5 var(--mono); color: #eef3f8;
}
label.block { display: grid; gap: 6px; margin: 12px 0; color: var(--ink); }
textarea, input[type=text] {
  padding: 10px; border: 1px solid var(--line); background: #fff; color: var(--ink);
}
.nodes { display: flex; flex-wrap: wrap; gap: 8px; margin: 12px 0; }
.node {
  min-width: 4.6rem; padding: 8px 10px; background: #fff;
  border: 1px solid var(--line); font-family: var(--mono); font-size: 13px; text-align: center;
}
.node b { display: block; color: var(--accent); font-size: 16px; }
.grid3 { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 10px; }
.curve { padding: 10px; border: 1px solid var(--line); background: #fff; }
.curve svg { display: block; width: 100%; height: 88px; }
.curve b { display: block; margin-top: 6px; font: 700 13px/1.3 var(--mono); }
.curve span { color: var(--muted); font-size: 12px; }
.attn {
  display: grid; grid-template-columns: auto repeat(3, 1fr); gap: 6px;
  max-width: 22rem; font-family: var(--mono); font-size: 13px; margin: 12px 0;
}
.attn span { color: var(--muted); padding: 6px; }
.attn button {
  background: #fff; color: var(--ink); border: 1px solid var(--line); min-height: 48px; cursor: pointer;
}
.attn button.masked { background: #1a2332; color: #dce6f2; border-color: #1a2332; }
.attn button.self { box-shadow: inset 0 0 0 2px var(--accent); }
.check-list label { display: flex; gap: 10px; align-items: flex-start; margin: 0 0 8px; color: var(--ink); }
.warn { color: var(--bad); }
.foot {
  width: var(--page); margin: 0 auto; padding: 22px 0 48px;
  display: flex; justify-content: space-between; gap: 12px;
  border-top: 1px solid var(--line); color: var(--dim); font-size: 13px;
}
.foot a { font: 700 11px/1 var(--mono); letter-spacing: 0.08em; text-decoration: none; color: var(--dim); }
.next { margin-top: 2.4rem; }
@media (max-width: 720px) {
  .path li, .grid3 { grid-template-columns: 1fr; }
}
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }
.home { color: var(--muted); text-decoration: none; font: 700 12px/1 var(--mono); letter-spacing: 0.08em; }
.progress { display:flex; flex-wrap:wrap; gap:8px 16px; font:700 12px/1.4 ui-monospace,monospace; width: var(--page); margin: 14px auto 0; }
.progress a { color: inherit; opacity:.55; text-decoration:none; }
.progress a[aria-current] { opacity:1; }
.teach p { color: inherit; }
.ex { margin:18px 0; padding:16px 18px; border-left:3px solid currentColor; font:14px/1.6 ui-monospace,monospace; }
.ex ol { margin: 8px 0 0; padding-left: 1.2rem; }
.ex li { margin: 6px 0; color: var(--muted); }
.lede { color: var(--ink); font-size: 17px; }
.leave { margin: 2.2rem 0 0; color: var(--muted); }
.hero-links { display: flex; flex-wrap: wrap; gap: 18px 28px; margin: 28px 0 0; }
.hero-links a { font-weight: 700; text-decoration: none; }
.teach h2, .do h2 { margin: 2.2rem 0 12px; color: var(--ink); }