:root {
  --paper: #f2efe6;
  --paper-2: #e8e4d8;
  --surface: #fffcf5;
  --ink: #0b1c2c;
  --ink-soft: #2a3d4f;
  --mut: #3d5161;
  --rule: #c5d0d9;
  --cyan: #0e7490;
  --cyan-dim: #0c5f75;
  --orange: #c2410c;
  --orange-ink: #1a0a00;
  --ok: #0f766e;
  --ko: #b91c1c;
  --warn: #92400e;
  --font: "Archivo", "Helvetica Neue", sans-serif;
  --serif: "Source Sans 3", "Segoe UI", sans-serif;
  --mono: "JetBrains Mono", ui-monospace, monospace;
  --measure: 68ch;
}

*, *::before, *::after { box-sizing: border-box; }
html { font-size: 18px; scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation: none !important; transition: none !important; }
}
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--serif);
  line-height: 1.55;
  min-height: 100vh;
}
a { color: var(--cyan); text-underline-offset: 0.15em; }
a:hover { color: var(--cyan-dim); }
a:focus-visible, button:focus-visible, input:focus-visible {
  outline: 2px solid var(--cyan);
  outline-offset: 3px;
}

.skip {
  position: absolute;
  left: 1rem;
  top: -3rem;
  background: var(--ink);
  color: var(--paper);
  padding: 0.5rem 0.8rem;
  z-index: 20;
}
.skip:focus { top: 0.6rem; }

.top {
  border-bottom: 1px solid var(--rule);
  background: var(--surface);
  position: sticky;
  top: 0;
  z-index: 8;
}
.top-inner, .wrap, .foot-inner {
  width: min(1120px, calc(100% - 2rem));
  margin: 0 auto;
}
.top-inner {
  display: flex;
  align-items: center;
  gap: 1rem;
  min-height: 56px;
}
.brand {
  font-family: var(--font);
  font-weight: 700;
  letter-spacing: -0.02em;
  color: var(--ink);
  text-decoration: none;
}
.brand span { color: var(--cyan); font-weight: 500; }
.top nav { margin-left: auto; display: flex; gap: 1rem; }
.top nav a { color: var(--ink-soft); text-decoration: none; font-family: var(--font); font-size: 0.88rem; font-weight: 600; }
.top nav a:hover { color: var(--cyan); }

.hero {
  padding: 2.4rem 0 1.6rem;
  border-bottom: 1px solid var(--rule);
}
.hero h1 {
  font-family: var(--font);
  font-size: clamp(1.7rem, 4vw, 2.45rem);
  line-height: 1.08;
  letter-spacing: -0.03em;
  margin: 0 0 0.7rem;
  max-width: 22ch;
}
.lede { max-width: var(--measure); color: var(--ink-soft); margin: 0 0 1.1rem; }
.meta {
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem 0.9rem;
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--mut);
}
.meta b { color: var(--ink); font-weight: 600; }

.btn {
  display: inline-flex;
  align-items: center;
  gap: 0.45rem;
  font-family: var(--font);
  font-weight: 700;
  font-size: 0.92rem;
  border: 1px solid var(--ink);
  background: var(--ink);
  color: var(--paper);
  padding: 0.7rem 1rem;
  text-decoration: none;
  cursor: pointer;
}
.btn:hover { background: var(--cyan); border-color: var(--cyan); color: #fff; }
.btn-ghost {
  background: transparent;
  color: var(--ink);
}
.btn-ghost:hover { background: var(--paper-2); color: var(--ink); }
.btn-orange {
  background: var(--orange);
  border-color: var(--orange);
  color: var(--orange-ink);
}
.btn-orange:hover { filter: brightness(1.05); color: var(--orange-ink); }

.notice {
  margin: 1.4rem 0;
  padding: 0.85rem 1rem;
  background: var(--paper-2);
  border: 1px solid var(--rule);
  max-width: 78ch;
}
.notice strong { font-family: var(--font); }
.notice.legal { font-size: 0.92rem; }

.grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1.6rem;
  padding: 1.6rem 0 3rem;
}
@media (min-width: 880px) {
  .grid { grid-template-columns: 280px 1fr; align-items: start; }
}

.toc {
  background: var(--surface);
  border: 1px solid var(--rule);
  padding: 0.9rem 0.85rem;
}
.toc h2 {
  font-family: var(--font);
  font-size: 0.82rem;
  margin: 0 0 0.6rem;
}
.toc ol { margin: 0; padding: 0; list-style: none; }
.toc a {
  display: grid;
  grid-template-columns: 2.2rem 1fr auto;
  gap: 0.4rem;
  padding: 0.42rem 0.3rem;
  text-decoration: none;
  color: var(--ink);
  font-size: 0.86rem;
  border-top: 1px solid transparent;
}
.toc a:hover, .toc a[aria-current="true"] { background: var(--paper-2); }
.toc a[aria-current="true"] { box-shadow: inset 3px 0 0 var(--cyan); }
.toc .n { font-family: var(--mono); font-size: 0.7rem; color: var(--cyan); }
.toc .h { font-family: var(--font); font-weight: 600; }
.toc .d { font-family: var(--mono); font-size: 0.68rem; color: var(--mut); }
.toc .done { color: var(--ok); }

.sheet {
  background: var(--surface);
  border: 1px solid var(--rule);
  padding: clamp(1.1rem, 2.4vw, 1.8rem);
  box-shadow: 0 10px 28px rgba(11, 28, 44, 0.06);
}
.sheet h2, .sheet h3 {
  font-family: var(--font);
  letter-spacing: -0.02em;
  line-height: 1.2;
}
.sheet h2 { font-size: 1.45rem; margin: 0 0 0.45rem; }
.sheet h3 { font-size: 1.08rem; margin: 1.5rem 0 0.4rem; }
.sheet p, .sheet li { max-width: var(--measure); }
.sheet ul, .sheet ol { padding-left: 1.15rem; }
.kicker-time {
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--mut);
  margin: 0 0 0.35rem;
}

.yt {
  margin: 1rem 0 1.2rem;
  background: #111;
}
.yt iframe {
  display: block;
  width: 100%;
  aspect-ratio: 16 / 9;
  border: 0;
  height: auto;
}
.yt-cap {
  font-size: 0.82rem;
  color: var(--mut);
  margin: 0.35rem 0 0;
}

.callout {
  margin: 1rem 0;
  padding: 0.8rem 0.95rem;
  background: #e7f3f6;
  border: 1px solid #b7d6de;
}
.callout.warn { background: #f6eedc; border-color: #e0c48a; }
.callout.ok { background: #e4f3ef; border-color: #9dcdc4; }

.ex {
  border: 1px dashed var(--cyan);
  padding: 0.85rem 1rem;
  margin: 1rem 0;
  background: #f7fbfc;
}
.ex h3 { margin-top: 0; }

.quiz { margin-top: 1.4rem; }
.q { margin: 0 0 1rem; padding: 0.8rem 0 0; border-top: 1px solid var(--rule); }
.q fieldset { border: 0; padding: 0; margin: 0; }
.q legend { font-family: var(--font); font-weight: 700; margin-bottom: 0.4rem; }
.q label { display: block; margin: 0.25rem 0; cursor: pointer; }
.q .fb { margin-top: 0.4rem; font-size: 0.9rem; }
.q .ok { color: var(--ok); }
.q .ko { color: var(--ko); }

.pager {
  display: flex;
  justify-content: space-between;
  gap: 0.8rem;
  margin-top: 1.6rem;
  flex-wrap: wrap;
}

.prog {
  height: 6px;
  background: var(--paper-2);
  border: 1px solid var(--rule);
}
.prog > span {
  display: block;
  height: 100%;
  background: var(--cyan);
  width: 0;
}

.catalog {
  padding: 1.6rem 0 3rem;
}
.course-lead {
  display: grid;
  gap: 1.2rem;
}
@media (min-width: 800px) {
  .course-lead { grid-template-columns: 1.4fr 0.8fr; }
}
.obj { columns: 1; }
@media (min-width: 720px) { .obj { columns: 2; } }
.obj li { break-inside: avoid; margin: 0 0 0.45rem; }

.mods {
  list-style: none;
  padding: 0;
  margin: 1.2rem 0 0;
}
.mods li {
  display: grid;
  grid-template-columns: 3.2rem 1fr auto;
  gap: 0.7rem;
  padding: 0.75rem 0;
  border-top: 1px solid var(--rule);
}
.mods .n { font-family: var(--mono); color: var(--cyan); font-size: 0.78rem; padding-top: 0.2rem; }
.mods h3 { margin: 0; font-family: var(--font); font-size: 1.02rem; }
.mods p { margin: 0.2rem 0 0; color: var(--ink-soft); font-size: 0.92rem; }
.mods .d { font-family: var(--mono); font-size: 0.72rem; color: var(--mut); align-self: center; }

.foot {
  border-top: 1px solid var(--rule);
  padding: 1.2rem 0 2rem;
  color: var(--mut);
  font-size: 0.85rem;
}

pre, code { font-family: var(--mono); font-size: 0.84em; }
pre {
  background: #111820;
  color: #e8eef4;
  padding: 0.8rem 0.9rem;
  overflow: auto;
  white-space: pre-wrap;
}