:root {
  --paper: #e6eef1;
  --paper-2: #d7e3e8;
  --ink: #142228;
  --ink-soft: #3a4d55;
  --rule: #9db0b7;
  --teal: #1b6b72;
  --teal-2: #2f8b8f;
  --ochre: #b85a28;
  --card: #f4f8f9;
  --shadow: 0 18px 40px rgba(20, 34, 40, 0.08);
  --mono: "IBM Plex Mono", ui-monospace, monospace;
  --sans: "IBM Plex Sans", ui-sans-serif, system-ui, sans-serif;
  --serif: "Spectral", "Iowan Old Style", Georgia, serif;
  --max: 72rem;
}

[data-theme="dark"] {
  --paper: #10171a;
  --paper-2: #182226;
  --ink: #e4eef1;
  --ink-soft: #a9bdc4;
  --rule: #3a4f56;
  --teal: #6ec4c8;
  --teal-2: #8fd4d4;
  --ochre: #e08a52;
  --card: #172024;
  --shadow: 0 18px 40px rgba(0, 0, 0, 0.35);
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #10171a;
    --paper-2: #182226;
    --ink: #e4eef1;
    --ink-soft: #a9bdc4;
    --rule: #3a4f56;
    --teal: #6ec4c8;
    --teal-2: #8fd4d4;
    --ochre: #e08a52;
    --card: #172024;
    --shadow: 0 18px 40px rgba(0, 0, 0, 0.35);
  }
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--serif);
  font-size: 1.125rem;
  line-height: 1.65;
  font-feature-settings: "onum" 1, "kern" 1;
}

.skip {
  position: absolute;
  left: -999px;
  top: 0;
  background: var(--teal);
  color: var(--paper);
  padding: 0.5rem 1rem;
}
.skip:focus { left: 0.5rem; top: 0.5rem; z-index: 20; }

.tapes {
  display: grid;
  grid-template-rows: auto auto;
  border-bottom: 1px solid var(--rule);
  background: var(--paper-2);
  font-family: var(--mono);
  font-size: 0.72rem;
  letter-spacing: 0.04em;
  overflow: hidden;
}
.tape {
  display: flex;
  gap: 1.4rem;
  white-space: nowrap;
  padding: 0.35rem 0.8rem;
  animation: marquee 48s linear infinite;
}
.tape.slow { animation-duration: 62s; opacity: 0.78; }
.tape b { color: var(--teal); font-weight: 500; }
.tape .up { color: var(--teal-2); }
.tape .dn { color: var(--ochre); }
@keyframes marquee {
  from { transform: translateX(0); }
  to { transform: translateX(-50%); }
}

.shell {
  display: grid;
  grid-template-columns: 16.5rem minmax(0, 1fr);
  max-width: 92rem;
  margin: 0 auto;
}

nav.toc {
  position: sticky;
  top: 0;
  align-self: start;
  height: 100dvh;
  overflow: auto;
  padding: 1.4rem 1.1rem 3rem;
  border-right: 1px solid var(--rule);
  font-family: var(--sans);
  font-size: 0.84rem;
}
nav.toc .brand {
  font-family: var(--serif);
  font-style: italic;
  font-size: 1.15rem;
  line-height: 1.2;
  margin: 0 0 0.35rem;
}
nav.toc .meta {
  color: var(--ink-soft);
  font-size: 0.75rem;
  margin-bottom: 1.1rem;
}
nav.toc a {
  display: block;
  color: var(--ink-soft);
  text-decoration: none;
  padding: 0.22rem 0;
}
nav.toc a:hover, nav.toc a[aria-current="true"] { color: var(--teal); }
nav.toc .ch { margin-top: 0.7rem; color: var(--ink); font-weight: 600; }

.tools {
  display: flex;
  gap: 0.4rem;
  margin: 1rem 0 0;
}
.tools button {
  font-family: var(--sans);
  font-size: 0.75rem;
  border: 1px solid var(--rule);
  background: transparent;
  color: var(--ink);
  padding: 0.28rem 0.55rem;
  cursor: pointer;
}
.tools button:focus-visible { outline: 2px solid var(--teal); outline-offset: 2px; }

main {
  padding: 2.4rem 7vw 6rem;
  max-width: 46rem;
}

.kicker {
  font-family: var(--sans);
  font-size: 0.78rem;
  letter-spacing: 0.16em;
  text-transform: uppercase;
  color: var(--teal);
  margin: 0 0 0.6rem;
}
h1 {
  font-weight: 300;
  font-size: clamp(2.3rem, 5vw, 3.6rem);
  line-height: 1.08;
  letter-spacing: -0.02em;
  margin: 0 0 0.8rem;
}
.subtitle {
  font-size: 1.2rem;
  color: var(--ink-soft);
  margin: 0 0 1.6rem;
}
h2 {
  font-weight: 500;
  font-size: 1.7rem;
  margin: 3.2rem 0 0.8rem;
  padding-top: 0.6rem;
}
h3 {
  font-weight: 600;
  font-size: 1.2rem;
  margin: 2rem 0 0.5rem;
}
p { margin: 0 0 1rem; }
a { color: var(--teal); }
code, .katex { font-size: 0.95em; }
code {
  font-family: var(--mono);
  font-size: 0.84em;
  background: var(--paper-2);
  padding: 0.05em 0.3em;
}

.box {
  background: var(--card);
  border-left: 3px solid var(--teal);
  padding: 0.85rem 1rem 0.4rem;
  margin: 1.2rem 0 1.4rem;
  box-shadow: var(--shadow);
}
.box.remark { border-left-color: var(--ochre); }
.box .lbl {
  font-family: var(--sans);
  font-size: 0.72rem;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--teal);
  margin: 0 0 0.35rem;
}
.box.remark .lbl { color: var(--ochre); }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.95rem;
  margin: 1rem 0 1.4rem;
}
th, td {
  text-align: left;
  border-bottom: 1px solid var(--rule);
  padding: 0.4rem 0.5rem 0.4rem 0;
  vertical-align: top;
}
th { font-family: var(--sans); font-size: 0.78rem; letter-spacing: 0.04em; }

.eq {
  overflow-x: auto;
  margin: 1rem 0 1.3rem;
  padding: 0.4rem 0;
}

.src {
  font-family: var(--mono);
  font-size: 0.72rem;
  color: var(--ink-soft);
}

footer {
  margin-top: 4rem;
  padding-top: 1rem;
  border-top: 1px solid var(--rule);
  font-family: var(--sans);
  font-size: 0.82rem;
  color: var(--ink-soft);
}

@media (max-width: 860px) {
  .shell { grid-template-columns: 1fr; }
  nav.toc {
    position: relative;
    height: auto;
    border-right: 0;
    border-bottom: 1px solid var(--rule);
    max-height: 40vh;
  }
  main { padding: 1.4rem 1.1rem 4rem; }
}

@media (prefers-reduced-motion: reduce) {
  .tape { animation: none; }
  html { scroll-behavior: auto; }
}