:root {
  --bg: #0e1c33;
  --bg-2: #162744;
  --ink: #e8eef8;
  --muted: #9bb3d0;
  --dim: #6d86a6;
  --line: #2a4568;
  --cyan: #9be7f2;
  --paper: #f4f7fb;
  --paper-ink: #122038;
  --paper-mute: #4a5d78;
  --ok: #7dba94;
  --bad: #e07a6a;
  --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(126, 164, 217, 0.09) 1px, transparent 1px),
    linear-gradient(90deg, rgba(126, 164, 217, 0.09) 1px, transparent 1px);
  background-size: 28px 28px, 28px 28px;
  font: 16px/1.75 var(--sans);
}
a { color: var(--cyan); text-underline-offset: 0.18em; }
a:focus-visible, button:focus-visible, input:focus-visible, textarea:focus-visible, select:focus-visible {
  outline: 2px solid var(--cyan); outline-offset: 3px;
}
button, input, textarea, select { font: inherit; color: inherit; }
.skip {
  position: absolute; left: 12px; top: 12px; z-index: 20;
  padding: 8px 12px; background: var(--cyan); color: var(--bg);
  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%, transparent);
  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(--cyan); }
main { width: var(--page); margin: 0 auto; padding: 2.6rem 0 4.5rem; }
.kicker { margin: 0 0 12px; color: var(--cyan); 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); }
.paper h2 { margin-top: 0; color: var(--paper-ink); }
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(--cyan); font: 700 12px/1.6 var(--mono); }
.path a { color: var(--ink); font-weight: 700; text-decoration: none; }
.path a:hover { color: var(--cyan); }
.path small { display: block; color: var(--muted); font-weight: 400; margin-top: 4px; }
.paper {
  margin: 1.6rem 0;
  padding: 28px 24px 22px;
  color: var(--paper-ink);
  background: var(--paper);
  box-shadow: 0 24px 60px rgba(0, 0, 0, 0.38);
  border: 1px solid #d5deea;
}
.paper p, .paper li { color: var(--paper-mute); }
.paper p.mud { color: var(--paper-ink); font-weight: 700; }
.sheet-meta {
  display: flex; justify-content: space-between; gap: 12px;
  margin: 0 0 16px;
  font: 700 11px/1 var(--mono); letter-spacing: 0.1em; color: #1a4f8a;
}
.choices, .impls { display: grid; gap: 8px; margin: 16px 0; }
.choices button, .impls button, .act {
  text-align: left; min-height: 46px; padding: 10px 14px;
  border: 1px solid var(--line); background: transparent; color: var(--ink); cursor: pointer;
}
.choices button:hover, .act:hover { border-color: var(--cyan); color: var(--cyan); }
.choices button.is-ok { border-color: var(--ok); color: var(--ok); }
.choices button.is-bad { border-color: var(--bad); color: var(--bad); }
.paper .choices button, .paper .act {
  border-color: #c5d0e0; color: var(--paper-ink); background: #fff;
}
.paper .choices button:hover, .paper .act:hover { border-color: #1a4f8a; color: #1a4f8a; }
.paper .choices button.is-ok { border-color: #2f6d4f; color: #2f6d4f; }
.paper .choices button.is-bad { border-color: #a33b32; color: #a33b32; }
.out {
  margin: 12px 0 0; padding: 12px 14px; background: var(--bg-2);
  border-left: 3px solid var(--cyan); color: var(--ink);
}
.out.is-ok { border-color: var(--ok); }
.out.is-bad { border-color: var(--bad); }
.paper .out { background: #e8eef6; color: var(--paper-ink); }
pre, .wire {
  overflow: auto; padding: 14px 16px; background: #0a1628;
  border: 1px solid var(--line); font: 13px/1.5 var(--mono); color: var(--ink);
}
.paper pre, .paper .wire { background: #122038; color: #e8eef8; }
.calc {
  margin: 14px 0;
  padding: 14px 16px;
  background: #122038;
  color: #e8eef8;
  font: 14px/1.6 var(--mono);
}
.calc .sum { color: var(--cyan); font-weight: 700; }
label.block { display: grid; gap: 6px; margin: 12px 0; color: var(--ink); }
.paper label.block { color: var(--paper-ink); }
textarea, input[type=text], input[type=number] {
  padding: 10px; border: 1px solid var(--line); background: var(--bg-2); color: var(--ink);
}
.paper textarea, .paper input[type=text], .paper input[type=number] {
  background: #fff; color: var(--paper-ink); border-color: #c5d0e0;
}
.quiz label, fieldset label { display: block; margin: 8px 0; cursor: pointer; }
fieldset { border: 1px solid #c5d0e0; margin: 10px 0 0; padding: 10px 12px; }
legend { font: 700 11px/1 var(--mono); color: #1a4f8a; }
.doodle { margin: 16px 0; padding: 12px; border: 1px dashed #c5d0e0; }
.doodle.is-salad { background: #f7ece8; }
.req { margin: 14px 0; padding: 12px; border: 1px solid #c5d0e0; background: #fff; }
.req p { margin: 0 0 8px; color: var(--paper-ink); }
.bins { display: flex; flex-wrap: wrap; gap: 8px; }
.bins button {
  min-height: 40px; padding: 8px 12px;
  border: 1px solid #c5d0e0; background: #fff; color: var(--paper-ink); cursor: pointer;
}
.bins button.is-ok { border-color: #2f6d4f; color: #2f6d4f; }
.bins button.is-bad { border-color: #a33b32; color: #a33b32; }
.cust { display: grid; grid-template-columns: 1fr 1fr; gap: 12px; margin-top: 12px; }
.cust article { padding: 12px; background: #fff; border: 1px solid #c5d0e0; }
.cust h3 { margin: 0 0 8px; font: 700 14px/1.3 var(--serif); }
.state { font: 700 12px/1 var(--mono); letter-spacing: 0.08em; }
.state.alive { color: #2f6d4f; }
.state.dead { color: #a33b32; }
.state.warn { color: #8a5a18; }
.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; }
.next { margin-top: 2.4rem; }
@media (max-width: 720px) {
  .path li, .cust { grid-template-columns: 1fr; }
}
main label { display: grid; gap: 6px; margin: 12px 0; }
main input, main textarea { padding: 8px 10px; border: 1px solid var(--line); background: #f4f7fb; color: inherit; }
.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); }
.paper .do h2 { color: var(--paper-ink); }