/* Didactical — site styles (2026-09-11)
   Palette: cool paper, graphite ink, one highlighter. Type: Archivo (expanded) for
   display, Public Sans (the US Web Design System face) for reading, IBM Plex Mono
   for citations and figures. */

:root {
  --paper: #EDF0F2;
  --surface: #FFFFFF;
  --ink: #15202B;
  --muted: #55606C;
  --rule: #CBD2D9;
  --mark: #F5D845;
  --mark-stroke: #F5D845;
  --mark-ink: #15202B;
  --signal: #2346C4;
  --deep: #15202B;
  --deep-ink: #EDF0F2;
  --deep-muted: #A7B1BC;
  --ok: #1F7A4D;
  --dev: #8A6A00;
  --btn-bg: #15202B;
  --btn-ink: #FFFFFF;

  --f-display: "Archivo", "Helvetica Neue", Arial, sans-serif;
  --f-body: "Public Sans", "Segoe UI", system-ui, -apple-system, sans-serif;
  --f-mono: "IBM Plex Mono", ui-monospace, "SFMono-Regular", Menlo, monospace;

  --t-xs: 0.8125rem;
  --t-sm: 0.9375rem;
  --t-md: 1.0625rem;
  --t-lg: 1.3125rem;
  --t-xl: 1.75rem;
  --t-2xl: 2.375rem;
  --t-3xl: clamp(2.5rem, 5.2vw, 3.875rem);

  --gutter: clamp(16px, 4vw, 40px);
  --max: 1160px;
  --radius: 6px;
}

@media (prefers-color-scheme: dark) {
  :root:not([data-theme="light"]) {
    --paper: #0D1218;
    --surface: #151C24;
    --ink: #E5E9EE;
    --muted: #99A3AF;
    --rule: #27313C;
    --mark: #D8BB35;
    --mark-stroke: rgba(216, 187, 53, 0.34);
    --mark-ink: #0D1218;
    --signal: #93A9FF;
    --deep: #18212C;
    --deep-ink: #E5E9EE;
    --deep-muted: #9AA5B2;
    --ok: #5CC28F;
    --dev: #E0BE4A;
    --btn-bg: #E5E9EE;
    --btn-ink: #0D1218;
  }
}
:root[data-theme="dark"] {
  --paper: #0D1218;
  --surface: #151C24;
  --ink: #E5E9EE;
  --muted: #99A3AF;
  --rule: #27313C;
  --mark: #D8BB35;
  --mark-stroke: rgba(216, 187, 53, 0.34);
  --mark-ink: #0D1218;
  --signal: #93A9FF;
  --deep: #18212C;
  --deep-ink: #E5E9EE;
  --deep-muted: #9AA5B2;
  --ok: #5CC28F;
  --dev: #E0BE4A;
  --btn-bg: #E5E9EE;
  --btn-ink: #0D1218;
}

*, *::before, *::after { box-sizing: border-box; }
html { -webkit-text-size-adjust: 100%; scroll-behavior: smooth; }
@media (prefers-reduced-motion: reduce) { html { scroll-behavior: auto; } }

body {
  margin: 0;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--f-body);
  font-size: var(--t-md);
  line-height: 1.6;
  text-rendering: optimizeLegibility;
}
img, svg, canvas { max-width: 100%; }
a { color: inherit; }
p { margin: 0; }
h1, h2, h3, h4 {
  margin: 0;
  font-family: var(--f-display);
  font-stretch: 118%;
  font-variation-settings: "wdth" 118;
  font-weight: 760;
  letter-spacing: -0.012em;
  line-height: 1.08;
  text-wrap: balance;
}
:focus-visible { outline: 3px solid var(--signal); outline-offset: 3px; border-radius: 2px; }

.wrap { max-width: var(--max); margin-inline: auto; padding-inline: var(--gutter); }

/* the highlighter — the one bold device on the site */
.hl {
  background-image: linear-gradient(transparent 58%, var(--mark-stroke) 58%, var(--mark-stroke) 94%, transparent 94%);
  padding-inline: 0.08em;
  -webkit-box-decoration-break: clone;
  box-decoration-break: clone;
}

.eyebrow {
  font-family: var(--f-mono);
  font-size: var(--t-xs);
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--muted);
}
.lede { font-size: var(--t-lg); line-height: 1.5; max-width: 38rem; color: var(--ink); }
.muted { color: var(--muted); }
.prose { max-width: 40rem; display: grid; gap: 1.1rem; }
.prose h2 { font-size: var(--t-xl); margin-top: 1.2rem; }
.prose h3 { font-size: var(--t-lg); margin-top: 0.6rem; }

/* ---------- header ---------- */
.site-head { border-bottom: 1px solid var(--rule); background: var(--paper); position: sticky; top: 0; z-index: 10; }
.site-head .wrap { display: flex; align-items: center; gap: 1.25rem; min-height: 68px; flex-wrap: wrap; padding-block: 10px; }
.wordmark {
  font-family: var(--f-display);
  font-variation-settings: "wdth" 125;
  font-stretch: 125%;
  font-weight: 800;
  font-size: 1.3rem;
  letter-spacing: -0.01em;
  text-decoration: none;
  margin-right: auto;
}
.wordmark span { background-image: linear-gradient(transparent 60%, var(--mark-stroke) 60%, var(--mark-stroke) 92%, transparent 92%); }
.nav { display: flex; align-items: center; gap: 0.25rem 1.1rem; flex-wrap: wrap; }
.nav a { text-decoration: none; font-size: var(--t-sm); font-weight: 500; color: var(--muted); padding-block: 4px; }
.nav a:hover { color: var(--ink); }
.nav a[aria-current="page"] { color: var(--ink); box-shadow: inset 0 -2px 0 var(--ink); }
.head-actions { display: flex; gap: 0.5rem; align-items: center; }

.btn {
  display: inline-flex; align-items: center; justify-content: center; gap: 0.5rem;
  font: 600 var(--t-sm)/1 var(--f-body);
  padding: 0.8rem 1.15rem;
  border-radius: var(--radius);
  text-decoration: none;
  border: 1px solid transparent;
  cursor: pointer;
  white-space: nowrap;
}
.btn-primary { background: var(--btn-bg); color: var(--btn-ink); }
.btn-primary:hover { filter: brightness(1.15); }
.btn-quiet { border-color: var(--rule); color: var(--ink); background: transparent; }
.btn-quiet:hover { border-color: var(--ink); }
.btn-sm { padding: 0.55rem 0.85rem; font-size: var(--t-xs); }
.btn-mark { background: var(--mark); color: var(--mark-ink); }
.btn-mark:hover { filter: brightness(1.05); }

@media (max-width: 760px) {
  .site-head { position: static; }
  .nav { order: 3; width: 100%; gap: 0.25rem 1rem; }
}

/* ---------- sections ---------- */
.section { padding-block: clamp(56px, 8vw, 104px); }
.section + .section { border-top: 1px solid var(--rule); }
.section-head { display: grid; gap: 0.75rem; margin-bottom: clamp(28px, 4vw, 48px); max-width: 44rem; }
.section-head h2 { font-size: var(--t-2xl); }

/* ---------- hero ---------- */
.hero { padding-block: clamp(40px, 6vw, 80px) clamp(56px, 7vw, 96px); }
.hero-grid { display: grid; grid-template-columns: minmax(0, 1.02fr) minmax(0, 1fr); gap: clamp(32px, 5vw, 72px); align-items: center; }
.hero h1 { font-size: var(--t-3xl); margin-block: 0.9rem 1.4rem; }
.hero .lede + .lede { margin-top: 1rem; font-size: var(--t-md); color: var(--muted); }
.cta-row { display: flex; gap: 0.75rem; flex-wrap: wrap; margin-top: 2rem; }
@media (max-width: 900px) { .hero-grid { grid-template-columns: 1fr; } }

.page-hero { padding-block: clamp(44px, 6vw, 84px) clamp(36px, 5vw, 64px); border-bottom: 1px solid var(--rule); }
.page-hero h1 { font-size: clamp(2.25rem, 4.6vw, 3.25rem); margin-block: 0.8rem 1.2rem; max-width: 22ch; }

/* ---------- the specimen: a manual page becoming a lesson ---------- */
.specimen { display: grid; gap: 0; filter: drop-shadow(0 18px 40px rgba(21, 32, 43, 0.12)); }
.sheet {
  background: var(--surface);
  border: 1px solid var(--rule);
  border-radius: var(--radius) var(--radius) 0 0;
  padding: 1.25rem 1.35rem 1.1rem;
  font-size: var(--t-sm);
}
.sheet-meta { display: flex; justify-content: space-between; gap: 1rem; flex-wrap: wrap; font-family: var(--f-mono); font-size: 0.72rem; color: var(--muted); border-bottom: 1px dashed var(--rule); padding-bottom: 0.6rem; margin-bottom: 0.8rem; }
.sheet ol { list-style: none; margin: 0; padding: 0; display: grid; gap: 0.6rem; }
.sheet li { display: grid; grid-template-columns: 5.4rem 1fr; gap: 0.6rem; line-height: 1.45; }
.sheet .cite { font-family: var(--f-mono); font-size: 0.72rem; color: var(--muted); padding-top: 0.15rem; }

.becomes {
  display: flex; align-items: center; gap: 0.6rem;
  background: var(--deep); color: var(--deep-ink);
  font-family: var(--f-mono); font-size: 0.72rem; letter-spacing: 0.06em; text-transform: uppercase;
  padding: 0.5rem 1.35rem;
}
.becomes svg { flex: none; }

.lesson {
  background: var(--surface);
  border: 1px solid var(--rule);
  border-top: 0;
  border-radius: 0 0 var(--radius) var(--radius);
  padding: 1.15rem 1.35rem 1.3rem;
  display: grid; gap: 0.95rem;
}
.lesson-top { display: flex; justify-content: space-between; align-items: baseline; gap: 0.75rem; flex-wrap: wrap; }
.lesson-title { font-family: var(--f-display); font-variation-settings: "wdth" 110; font-weight: 700; font-size: 1.05rem; }
.seg { display: inline-flex; border: 1px solid var(--rule); border-radius: 999px; padding: 2px; font-size: 0.75rem; }
.seg span { padding: 0.2rem 0.65rem; border-radius: 999px; color: var(--muted); }
.seg .on { background: var(--btn-bg); color: var(--btn-ink); }
.player { display: grid; grid-template-columns: auto 1fr auto; gap: 0.8rem; align-items: center; }
.play { width: 36px; height: 36px; border-radius: 50%; background: var(--btn-bg); display: grid; place-items: center; }
.play svg { fill: var(--btn-ink); }
.wave { height: 40px; width: 100%; display: block; }
.time { font-family: var(--f-mono); font-size: 0.72rem; color: var(--muted); font-variant-numeric: tabular-nums; }
.voices { display: flex; gap: 1rem; font-size: 0.75rem; color: var(--muted); flex-wrap: wrap; }
.voices i { display: inline-block; width: 8px; height: 8px; border-radius: 50%; margin-right: 0.35rem; vertical-align: 0; }
.quiz { border-top: 1px dashed var(--rule); padding-top: 0.9rem; display: grid; gap: 0.55rem; font-size: var(--t-sm); }
.quiz-q { font-weight: 600; line-height: 1.4; }
.choice { display: flex; gap: 0.6rem; align-items: center; padding: 0.45rem 0.65rem; border: 1px solid var(--rule); border-radius: var(--radius); font-size: 0.875rem; }
.choice b { font-family: var(--f-mono); font-weight: 500; font-size: 0.75rem; color: var(--muted); }
.choice.miss { border-color: var(--dev); }
.choice.miss b { color: var(--dev); }
.correction { font-size: 0.8125rem; color: var(--muted); display: flex; gap: 0.5rem; align-items: baseline; }
.correction strong { color: var(--ink); font-weight: 600; }

/* ---------- the loop (a real sequence, so it is numbered) ---------- */
.loop { list-style: none; margin: 0; padding: 0; display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); border-top: 1px solid var(--ink); }
.loop li { padding: 1.4rem 1.4rem 1.6rem 0; border-bottom: 1px solid var(--rule); display: grid; gap: 0.5rem; align-content: start; }
.loop li:not(:nth-child(3n+1)) { padding-left: 1.4rem; border-left: 1px solid var(--rule); }
.loop .n { font-family: var(--f-mono); font-size: var(--t-xs); color: var(--muted); }
.loop h3 { font-size: var(--t-lg); }
.loop p { color: var(--muted); font-size: var(--t-sm); max-width: 32ch; }
@media (max-width: 860px) {
  .loop { grid-template-columns: 1fr; }
  .loop li, .loop li:not(:nth-child(3n+1)) { padding: 1.2rem 0; border-left: 0; }
}

/* ---------- figures band ---------- */
.band { background: var(--deep); color: var(--deep-ink); }
.band .eyebrow { color: var(--deep-muted); }
.figures { display: grid; grid-template-columns: minmax(0, 1.7fr) repeat(3, minmax(0, 1fr)); gap: clamp(20px, 3vw, 40px); align-items: end; }
.figures .src h2 { font-size: var(--t-xl); margin-top: 0.6rem; }
.figures .src p { color: var(--deep-muted); margin-top: 0.75rem; font-size: var(--t-sm); max-width: 34ch; }
.fig { border-top: 1px solid var(--deep-muted); padding-top: 0.9rem; }
.fig .num { font-family: var(--f-display); font-variation-settings: "wdth" 125; font-weight: 800; font-size: clamp(2.75rem, 5vw, 4rem); line-height: 1; font-variant-numeric: tabular-nums; }
.fig .lbl { color: var(--deep-muted); font-size: var(--t-sm); margin-top: 0.4rem; }
@media (max-width: 860px) { .figures { grid-template-columns: repeat(3, minmax(0, 1fr)); } .figures .src { grid-column: 1 / -1; } }
@media (max-width: 460px) { .figures { grid-template-columns: 1fr; } }

/* ---------- two-up and three-up ---------- */
.two { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: clamp(20px, 3vw, 40px); }
.three { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: clamp(20px, 3vw, 36px); }
@media (max-width: 860px) { .two, .three { grid-template-columns: 1fr; } }

.format { display: grid; gap: 0.7rem; align-content: start; padding-top: 1.1rem; border-top: 3px solid var(--ink); }
.format h3 { font-size: var(--t-xl); }
.format p { color: var(--muted); max-width: 38ch; }
.format .tag { font-family: var(--f-mono); font-size: var(--t-xs); color: var(--muted); }

.audience { display: grid; gap: 0.6rem; align-content: start; }
.audience h3 { font-size: var(--t-lg); }
.audience p { color: var(--muted); font-size: var(--t-sm); }
.audience .eyebrow { margin-bottom: 0.2rem; }

/* ---------- status ledger ---------- */
.ledger { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: clamp(20px, 3vw, 40px); }
.ledger h3 { font-size: var(--t-md); font-family: var(--f-mono); font-variation-settings: normal; font-stretch: normal; font-weight: 500; letter-spacing: 0.04em; text-transform: uppercase; display: flex; align-items: center; gap: 0.5rem; padding-bottom: 0.7rem; border-bottom: 1px solid var(--ink); }
.ledger ul { list-style: none; margin: 0; padding: 0; }
.ledger li { padding: 0.7rem 0; border-bottom: 1px solid var(--rule); font-size: var(--t-sm); display: grid; grid-template-columns: 1fr; gap: 0.15rem; }
.ledger li span { color: var(--muted); font-size: var(--t-xs); }
.dot { width: 9px; height: 9px; border-radius: 50%; display: inline-block; }
.dot.ok { background: var(--ok); }
.dot.dev { background: transparent; border: 2px solid var(--dev); }
@media (max-width: 760px) { .ledger { grid-template-columns: 1fr; } }

/* ---------- callout rows ---------- */
.split { display: grid; grid-template-columns: minmax(0, 0.9fr) minmax(0, 1.1fr); gap: clamp(28px, 5vw, 72px); align-items: start; }
@media (max-width: 860px) { .split { grid-template-columns: 1fr; } }

.defs { margin: 0; display: grid; gap: 0; border-top: 1px solid var(--ink); }
.defs div { display: grid; grid-template-columns: minmax(0, 12rem) minmax(0, 1fr); gap: 1rem; padding: 1rem 0; border-bottom: 1px solid var(--rule); }
.defs dt { font-weight: 650; }
.defs dd { margin: 0; color: var(--muted); font-size: var(--t-sm); }
@media (max-width: 560px) { .defs div { grid-template-columns: 1fr; gap: 0.25rem; } }

.pull {
  font-family: var(--f-display); font-variation-settings: "wdth" 112; font-weight: 650;
  font-size: clamp(1.5rem, 3vw, 2.125rem); line-height: 1.2; letter-spacing: -0.01em; max-width: 30ch; text-wrap: balance;
}

/* ---------- closing CTA ---------- */
.closer { background: var(--deep); color: var(--deep-ink); }
.closer .wrap { display: flex; justify-content: space-between; align-items: center; gap: 1.5rem 3rem; flex-wrap: wrap; padding-block: clamp(48px, 7vw, 88px); }
.closer h2 { font-size: var(--t-2xl); max-width: 20ch; }
.closer p { color: var(--deep-muted); margin-top: 0.8rem; max-width: 42ch; }

/* ---------- forms ---------- */
.form { display: grid; gap: 1.1rem; background: var(--surface); border: 1px solid var(--rule); border-radius: var(--radius); padding: clamp(20px, 3vw, 32px); }
.form .row { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 1.1rem; }
@media (max-width: 600px) { .form .row { grid-template-columns: 1fr; } }
.field { display: grid; gap: 0.4rem; }
.field label { font-size: var(--t-sm); font-weight: 600; }
.field .hint { font-size: var(--t-xs); color: var(--muted); font-weight: 400; }
.field input, .field select, .field textarea {
  font: inherit; font-size: var(--t-md); color: var(--ink); background: var(--paper);
  border: 1px solid var(--rule); border-radius: var(--radius); padding: 0.7rem 0.8rem; width: 100%;
}
.field textarea { min-height: 9rem; resize: vertical; }
.field input:focus, .field select:focus, .field textarea:focus { outline: 2px solid var(--signal); outline-offset: 1px; border-color: transparent; }
.hp { position: absolute; left: -10000px; width: 1px; height: 1px; overflow: hidden; }
.form-status { font-size: var(--t-sm); padding: 0.75rem 0.9rem; border-radius: var(--radius); border: 1px solid var(--rule); }
.form-status.ok { border-color: var(--ok); }
.form-status.err { border-color: var(--dev); }

.steps { list-style: none; margin: 0; padding: 0; display: grid; gap: 0; border-top: 1px solid var(--ink); counter-reset: s; }
.steps li { padding: 1rem 0 1rem 2.4rem; border-bottom: 1px solid var(--rule); position: relative; font-size: var(--t-sm); counter-increment: s; }
.steps li::before { content: counter(s); position: absolute; left: 0; top: 1rem; font-family: var(--f-mono); font-size: var(--t-xs); color: var(--muted); }
.steps li strong { display: block; font-size: var(--t-md); margin-bottom: 0.15rem; }

/* ---------- footer ---------- */
.site-foot { border-top: 1px solid var(--rule); padding-block: 40px 56px; font-size: var(--t-sm); color: var(--muted); }
.site-foot .wrap { display: grid; grid-template-columns: minmax(0, 1.4fr) repeat(2, minmax(0, 1fr)); gap: 2rem; }
.site-foot h4 { font-family: var(--f-mono); font-variation-settings: normal; font-stretch: normal; font-weight: 500; font-size: var(--t-xs); letter-spacing: 0.06em; text-transform: uppercase; color: var(--muted); margin-bottom: 0.7rem; }
.site-foot ul { list-style: none; margin: 0; padding: 0; display: grid; gap: 0.35rem; }
.site-foot a { text-decoration: none; color: var(--ink); }
.site-foot a:hover { text-decoration: underline; }
.site-foot .fine { margin-top: 0.9rem; font-size: var(--t-xs); max-width: 44ch; }
@media (max-width: 700px) { .site-foot .wrap { grid-template-columns: 1fr 1fr; } .site-foot .wrap > :first-child { grid-column: 1 / -1; } }

.skip { position: absolute; left: -10000px; }
.skip:focus { left: 16px; top: 12px; z-index: 50; background: var(--surface); padding: 0.5rem 0.8rem; border-radius: var(--radius); }