:root {
  --ink: #10131a;
  --paper: #f6f4ee;
  --line: #d7d2c6;
  --accent: #2b6cff;
  --muted: #6b6659;
  --card: #ffffff;
  --mono: ui-monospace, "SF Mono", "Cascadia Code", Menlo, monospace;
}
* { box-sizing: border-box; }
html { color-scheme: light; }
body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font: 16px/1.65 -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, sans-serif;
}
a { color: var(--accent); }

header {
  padding: 3.5rem 1.5rem 1rem;
  max-width: 720px;
  margin: 0 auto;
}
header .eyebrow {
  font-family: var(--mono); font-size: .78rem; letter-spacing: .08em;
  text-transform: uppercase; color: var(--muted); margin: 0 0 .8rem;
}
header h1 {
  font-size: 2.1rem; line-height: 1.15; margin: 0 0 .6rem; letter-spacing: -0.025em;
}
header .intro { font-size: 1.08rem; margin: 0 0 1rem; max-width: 60ch; }
header .intro:last-of-type { margin-bottom: 0; }
header .intro strong { font-weight: 600; }

.how { max-width: 720px; margin: 1.5rem auto 0; padding: 0 1.5rem; }
.how ol {
  margin: 0; padding: 1.1rem 1.1rem 1.1rem 2.4rem;
  border: 1px solid var(--line); border-radius: 10px; background: var(--card);
  font-size: .95rem;
}
.how li { margin: .3rem 0; }
.how li strong { font-weight: 600; }

/* Landing-page table of contents */
.toc { max-width: 720px; margin: 2.5rem auto 0; padding: 0 1.5rem; display: grid; gap: 1rem; }
.toc a {
  display: block; text-decoration: none; color: inherit;
  border: 1px solid var(--line); border-radius: 10px; padding: 1rem 1.2rem;
  background: var(--card); transition: border-color .15s ease;
}
.toc a:hover { border-color: var(--accent); }
.toc .t-num { font-family: var(--mono); font-size: .8rem; color: var(--accent); letter-spacing: .04em; }
.toc h2 { font-size: 1.15rem; margin: .15rem 0 .3rem; letter-spacing: -0.015em; }
.toc p { color: var(--muted); margin: 0; font-size: .95rem; }

/* A lesson section (single-page) or a lesson page's body */
.module, .lesson { max-width: 720px; margin: 2.5rem auto 0; padding: 0 1.5rem; }
.lesson { margin-top: 2rem; }
.num, .module .num {
  font-family: var(--mono); font-size: .8rem; color: var(--accent); letter-spacing: .04em;
}
.module h2, .lesson h2 { font-size: 1.3rem; margin: .15rem 0 .4rem; letter-spacing: -0.015em; }
.lede { color: var(--muted); margin: 0 0 1rem; max-width: 62ch; }
.try { font-size: .93rem; margin: 0 0 1rem; }
.try strong { font-weight: 600; }

.stage { border: 1px solid var(--line); border-radius: 10px; overflow: hidden; background: #000; }
canvas { display: block; width: 100%; height: 360px; }

.ctl-panel {
  display: flex; flex-wrap: wrap; gap: 1rem 1.5rem;
  padding: 1rem; margin-top: .75rem;
  border: 1px solid var(--line); border-radius: 10px; background: var(--card);
}
.ctl { display: flex; align-items: center; gap: .5rem; font-size: .9rem; }
.ctl-label { color: var(--muted); }
.ctl-value { font-family: var(--mono); font-size: .8rem; min-width: 3ch; }
.ctl-slider input { width: 160px; }
select { font: inherit; padding: .2rem .3rem; }

.fallback {
  padding: 2rem; text-align: center; color: var(--muted);
  font-family: var(--mono); font-size: .9rem; line-height: 1.7;
}

/* Long-form technical prose on a lesson page */
.prose { max-width: 720px; margin: 0 auto; padding: 0 1.5rem; }
.prose h3 { font-size: 1.05rem; margin: 2rem 0 .5rem; letter-spacing: -0.01em; }
.prose p { margin: 0 0 1rem; max-width: 64ch; }
.prose strong { font-weight: 600; }
.prose code {
  font-family: var(--mono); font-size: .85em;
  background: #ece7dc; padding: .05em .32em; border-radius: 4px;
}

/* Hand-authored SVG diagrams + JS-generated swatch strips */
figure.diagram { margin: 1.5rem 0; text-align: center; }
figure.diagram svg { max-width: 100%; height: auto; }
figcaption { color: var(--muted); font-size: .85rem; margin-top: .6rem; line-height: 1.5; }

.swatch-row { margin: .7rem 0; }
.swatch-row .label { font-size: .8rem; color: var(--muted); margin-bottom: .25rem; }
.swatch-strip {
  display: flex; height: 46px;
  border: 1px solid var(--line); border-radius: 6px; overflow: hidden;
}
.swatch-strip > div { flex: 1 1 0; }

/* Prev / next / home navigation on a lesson page */
.lesson-nav {
  max-width: 720px; margin: 2.5rem auto 0; padding: 0 1.5rem;
  display: flex; justify-content: space-between; gap: 1rem; font-size: .9rem;
}
.lesson-nav a { text-decoration: none; }
.lesson-nav .spacer { color: var(--muted); }

footer {
  max-width: 720px; margin: 4rem auto 3rem; padding: 1.5rem;
  border-top: 1px solid var(--line); color: var(--muted); font-size: .88rem;
}
footer a { color: var(--muted); }