/* ============================================================================
   Fiber & FTTx Course — design system
   Vinxi / Lepton house style: Hanken Grotesk + Geist Mono, midnight ink on
   snow, blue accent, sharp geometry, mono-uppercase labels.
   Tokens mirror @vinxi/design (brand.css). Authored once; every page uses it.
   ========================================================================== */

/* ---------- Self-hosted brand fonts ---------- */
@font-face {
  font-family: 'Hanken Grotesk';
  font-style: normal; font-weight: 300 700; font-display: swap;
  src: url('fonts/HankenGrotesk-Variable.woff2') format('woff2-variations'),
       url('fonts/HankenGrotesk-Variable.woff2') format('woff2');
}
@font-face {
  font-family: 'Geist Mono';
  font-style: normal; font-weight: 400 500; font-display: swap;
  src: url('fonts/GeistMono-Regular.woff2') format('woff2');
}

/* ---------- Design tokens (Vinxi brand) ---------- */
:root {
  /* surfaces */
  --bg:            #FBFDFF;   /* snow */
  --bg-soft:       #F2F5F9;   /* snow-dim */
  --bg-sunken:     #E9EEF5;
  /* ink */
  --ink:           #1A2040;   /* midnight — body */
  --ink-strong:    #14193A;   /* midnight-deep — headings */
  --ink-soft:      #6B7280;   /* steel — muted */
  --ink-faint:     #8E94A6;   /* ash */
  --slate:         #3D4566;
  --graphite:      #4F5670;
  /* borders */
  --line:          #DFE3EA;   /* silver */
  --line-strong:   #C9D0DB;
  --fog:           #E4ECF5;
  /* accent */
  --primary:       #0066E3;   /* blue */
  --primary-dark:  #0055C0;
  --primary-soft:  #E8F0FE;   /* blue-tint */
  --accent:        #0066E3;
  --accent-soft:   #E8F0FE;

  /* callout / semantic hues */
  --key:           #0055C0;   --key-soft:    #E8F0FE;
  --info:          #0066E3;   --info-soft:   #EEF4FE;
  --pitfall:       #C8362F;   --pitfall-soft:#FBECEB;
  --example:       #1F8855;   --example-soft:#E8F5EE;
  --analogy:       #B57E00;   --analogy-soft:#FCF3DF;
  --numbers:       #1A2040;   --numbers-soft:#F2F5F9;

  --ok:            #1F8855;
  --bad:           #C8362F;

  /* type */
  --font-sans: 'Hanken Grotesk', -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  --font-mono: 'Geist Mono', 'SF Mono', 'JetBrains Mono', Consolas, monospace;

  /* geometry — sharp */
  --radius:    3px;
  --radius-sm: 2px;
  --shadow:    0 1px 2px rgba(26,32,64,.04), 0 4px 12px rgba(26,32,64,.06);
  --shadow-sm: 0 1px 2px rgba(26,32,64,.05);
  --shadow-lg: 0 16px 32px rgba(26,32,64,.10);

  --ease: cubic-bezier(0.2, 0.8, 0.2, 1);

  --sidebar-w: 300px;
  --content-max: 820px;
}

/* ---------- Reset / base ---------- */
*, *::before, *::after { box-sizing: border-box; }
html { scroll-behavior: smooth; -webkit-text-size-adjust: 100%; }
body {
  margin: 0;
  font-family: var(--font-sans);
  font-size: 16px;
  line-height: 1.6;
  letter-spacing: -0.1px;
  color: var(--ink);
  background: var(--bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  text-rendering: optimizeLegibility;
}
@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  * { animation-duration: .001ms !important; transition-duration: .001ms !important; }
}

a { color: var(--primary); text-decoration: none; }
a:hover { color: var(--primary-dark); text-decoration: underline; }
code, kbd, samp { font-family: var(--font-mono); font-size: .88em; }
:not(pre) > code {
  background: var(--bg-soft); color: var(--primary-dark);
  padding: .1em .4em; border-radius: 2px; border: 1px solid var(--line);
  letter-spacing: -0.2px;
}
img, svg { max-width: 100%; }
hr { border: 0; border-top: 1px solid var(--line); margin: 2.5rem 0; }

/* thin brand scrollbars */
*::-webkit-scrollbar { width: 7px; height: 7px; }
*::-webkit-scrollbar-track { background: transparent; }
*::-webkit-scrollbar-thumb { background: var(--line-strong); }
*::-webkit-scrollbar-thumb:hover { background: var(--ink-faint); }

/* shared mono-label primitive */
.label, .module-eyebrow, .topbar__meta, .stat__label, .nav__subs,
.widget__bar, .pill, .module-footer .dir {
  font-family: var(--font-mono);
}

/* ---------- App layout ---------- */
.course-shell { display: flex; min-height: 100vh; }

.sidebar {
  width: var(--sidebar-w); flex: 0 0 var(--sidebar-w);
  background: var(--bg); border-right: 1px solid var(--line);
  position: sticky; top: 0; height: 100vh; overflow-y: auto; z-index: 30;
}
.sidebar__brand {
  display: flex; align-items: center; gap: .7rem;
  padding: 1.05rem 1.25rem; border-bottom: 1px solid var(--line);
  position: sticky; top: 0; background: var(--bg); z-index: 2;
}
/* square-in-square brand mark (Vinxi nav-logo-mark) */
.sidebar__brand .logo {
  width: 28px; height: 28px; flex: 0 0 28px;
  background: var(--ink-strong); position: relative; border-radius: 0; font-size: 0;
}
.sidebar__brand .logo::after { content: ""; position: absolute; inset: 6px; background: var(--primary); }
.sidebar__brand b { color: var(--ink-strong); font-size: .9rem; line-height: 1.15; letter-spacing: -0.3px; font-weight: 600; }
.sidebar__brand span { display: block; color: var(--ink-soft); font-size: .7rem; font-weight: 500; letter-spacing: -0.1px; }

.nav { padding: .75rem .6rem 3rem; }
.nav a.nav__item {
  display: flex; align-items: flex-start; gap: .6rem;
  padding: .5rem .6rem; border-radius: var(--radius-sm);
  color: var(--slate); font-size: .9rem; line-height: 1.35; font-weight: 500;
  border-left: 2px solid transparent;
}
.nav a.nav__item:hover { background: var(--bg-soft); color: var(--ink-strong); text-decoration: none; }
.nav a.nav__item.is-active { background: var(--primary-soft); color: var(--primary-dark); font-weight: 600; border-left-color: var(--primary); }
.nav__num {
  flex: 0 0 1.5rem; height: 1.5rem; display: grid; place-items: center;
  font-family: var(--font-mono); font-size: .72rem; font-weight: 500; border-radius: var(--radius-sm);
  background: var(--bg-soft); color: var(--ink-soft); border: 1px solid var(--line);
}
.nav a.is-active .nav__num { background: var(--primary); color: #fff; border-color: var(--primary); }
.nav a.is-done .nav__num { background: var(--ok); color: #fff; border-color: var(--ok); }
.nav__subs { list-style: none; margin: .15rem 0 .4rem 2.15rem; padding: 0; border-left: 1px solid var(--line); }
.nav__subs a { display: block; padding: .25rem .6rem; font-size: .76rem; font-family: var(--font-mono);
  letter-spacing: -0.2px; color: var(--ink-soft); border-radius: 2px; }
.nav__subs a:hover { color: var(--primary); background: var(--bg-soft); text-decoration: none; }

/* ---------- Topbar + reading progress ---------- */
.topbar {
  position: sticky; top: 0; z-index: 20;
  display: flex; align-items: center; gap: .75rem;
  background: rgba(251,253,255,.85); backdrop-filter: blur(8px);
  border-bottom: 1px solid var(--line); padding: .55rem 1.25rem; min-height: 52px;
}
.topbar__title { font-family: var(--font-mono); font-weight: 500; color: var(--ink-strong);
  font-size: .78rem; text-transform: uppercase; letter-spacing: .04em; }
.topbar__spacer { flex: 1; }
.topbar__meta { color: var(--ink-soft); font-size: .68rem; text-transform: uppercase; letter-spacing: .06em; font-weight: 500; }
.progress-track { position: absolute; left: 0; bottom: -1px; height: 2px; width: 100%; background: transparent; }
.progress-fill { height: 100%; width: 0; background: var(--primary); transition: width .1s linear; }

.menu-btn { display: none; background: var(--bg); border: 1px solid var(--line); border-radius: var(--radius-sm);
  width: 38px; height: 38px; cursor: pointer; font-size: 1.1rem; color: var(--ink); }

/* ---------- Content column ---------- */
.content { flex: 1 1 auto; min-width: 0; }
.module-main { max-width: var(--content-max); margin: 0 auto; padding: 2.5rem 1.75rem 5rem; }

.module-eyebrow { color: var(--primary); font-weight: 500; font-size: .72rem; letter-spacing: .14em;
  text-transform: uppercase; }
.module-main h1 { font-family: var(--font-sans); font-size: 2.45rem; font-weight: 500; line-height: 1.05;
  color: var(--ink-strong); margin: .4rem 0 .55rem; letter-spacing: -1.3px; }
.module-main h2 { font-family: var(--font-sans); font-size: 1.6rem; font-weight: 500; color: var(--ink-strong);
  margin: 2.7rem 0 .9rem; letter-spacing: -0.7px; line-height: 1.15; scroll-margin-top: 70px; }
.module-main h3 { font-family: var(--font-sans); font-size: 1.18rem; font-weight: 600; color: var(--ink-strong);
  margin: 1.8rem 0 .6rem; letter-spacing: -0.3px; scroll-margin-top: 70px; }
.module-main h2 + h3 { margin-top: 1rem; }
.module-main p { margin: 0 0 1.1rem; }
.lead { font-size: 1.2rem; line-height: 1.55; color: var(--slate); font-weight: 400; margin: 0 0 1.5rem; letter-spacing: -0.3px; }

.module-main ul, .module-main ol { margin: 0 0 1.2rem; padding-left: 1.4rem; }
.module-main li { margin: .35rem 0; }
.module-main li::marker { color: var(--ink-faint); }

.anchor-link { opacity: 0; margin-left: .4rem; font-weight: 400; color: var(--line-strong); text-decoration: none; }
h2:hover .anchor-link, h3:hover .anchor-link { opacity: 1; }

/* inline emphasis */
.key-term { font-weight: 600; color: var(--ink-strong); box-shadow: inset 0 -0.5em 0 var(--primary-soft); }
mark { background: var(--analogy-soft); padding: .05em .25em; border-radius: 2px; }
.pill { display: inline-block; font-size: .64rem; font-weight: 500; letter-spacing: .06em; text-transform: uppercase;
  padding: .15rem .5rem; border-radius: var(--radius-sm); background: var(--bg); color: var(--ink-soft);
  border: 1px solid var(--line); vertical-align: middle; }
.pill--std { background: var(--bg); color: var(--primary); border-color: var(--primary); }
.pill--typ { background: var(--bg); color: var(--analogy); border-color: var(--analogy); }
.pill--new { background: var(--bg); color: var(--example); border-color: var(--example); }

/* ---------- Learning objectives + recap ---------- */
.objectives, .recap {
  border: 1px solid var(--line); border-left: 3px solid var(--primary); border-radius: var(--radius);
  background: var(--bg-soft); padding: 1.1rem 1.25rem 1.1rem 1.4rem; margin: 0 0 2rem;
}
.objectives h2, .recap h2 { margin: 0 0 .5rem; font-size: 1.05rem; }
.objectives ul, .recap ul { margin: 0; padding-left: 1.2rem; }
.recap { background: var(--primary-soft); border-color: var(--primary); margin-top: 3rem; }

/* ---------- Callouts ---------- */
.callout {
  position: relative; border: 1px solid var(--line); border-left-width: 3px;
  border-radius: var(--radius); background: var(--bg-soft);
  padding: 1rem 1.15rem 1rem 1.2rem; margin: 1.5rem 0;
}
.callout__title { display: flex; align-items: center; gap: .5rem;
  font-weight: 600; color: var(--ink-strong); margin: 0 0 .35rem; font-size: .98rem; letter-spacing: -0.2px; }
.callout__title .ico { font-size: 1.1rem; line-height: 1; }
.callout > :last-child { margin-bottom: 0; }
.callout--key     { border-left-color: var(--key);     background: var(--key-soft); }
.callout--info    { border-left-color: var(--info);    background: var(--info-soft); }
.callout--pitfall { border-left-color: var(--pitfall); background: var(--pitfall-soft); }
.callout--example { border-left-color: var(--example); background: var(--example-soft); }
.callout--analogy { border-left-color: var(--analogy); background: var(--analogy-soft); }
.callout--numbers { border-left-color: var(--numbers); background: var(--numbers-soft); }

/* ---------- Cards ---------- */
.card-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(230px, 1fr)); gap: 1rem; margin: 1.5rem 0; }
.card { border: 1px solid var(--line); border-radius: var(--radius); background: var(--bg); padding: 1.1rem 1.15rem; box-shadow: var(--shadow-sm); }
.card h3, .card h4 { margin: 0 0 .4rem; font-size: 1rem; color: var(--ink-strong); letter-spacing: -0.3px; }
.card p { margin: 0; font-size: .92rem; color: var(--graphite); }
.card__ico { font-size: 1.5rem; display: block; margin-bottom: .4rem; }

/* ---------- Stat / "by the numbers" ---------- */
.stat-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(150px, 1fr)); gap: 1rem; margin: 1.5rem 0; }
.stat { text-align: center; border: 1px solid var(--line); border-radius: var(--radius); padding: 1rem .75rem; background: var(--bg-soft); }
.stat__num { font-family: var(--font-sans); font-size: 2rem; font-weight: 500; color: var(--primary-dark); line-height: 1;
  letter-spacing: -1px; font-variant-numeric: tabular-nums; }
.stat__label { display: block; margin-top: .45rem; font-size: .66rem; color: var(--ink-soft); text-transform: uppercase; letter-spacing: .06em; font-weight: 500; }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; margin: 1.5rem 0; border: 1px solid var(--line); border-radius: var(--radius); }
table.data-table { width: 100%; border-collapse: collapse; font-size: .92rem; }
.data-table th, .data-table td { padding: .6rem .8rem; text-align: left; border-bottom: 1px solid var(--line); }
.data-table thead th { background: var(--bg-soft); color: var(--ink-soft); font-family: var(--font-mono); font-weight: 500;
  position: sticky; top: 0; font-size: .68rem; text-transform: uppercase; letter-spacing: .05em; }
.data-table tbody td { color: var(--ink); }
.data-table tbody tr:hover { background: var(--bg-soft); }
.data-table tbody tr:last-child td { border-bottom: 0; }
.data-table td.num, .data-table th.num { font-family: var(--font-mono); font-variant-numeric: tabular-nums; letter-spacing: -0.2px; white-space: nowrap; }

/* ---------- Figures / diagrams ---------- */
.figure { margin: 1.75rem 0; }
.figure__frame { border: 1px solid var(--line); border-radius: var(--radius); background: var(--bg);
  padding: 1.25rem; box-shadow: var(--shadow-sm); overflow-x: auto; }
.figure__caption { margin-top: .6rem; font-size: .82rem; color: var(--ink-soft); text-align: center; }
.figure__caption b { color: var(--ink); }

pre.flow { font-family: var(--font-mono); font-size: .8rem; line-height: 1.5; color: var(--ink-strong);
  background: var(--bg-soft); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 1.1rem; overflow-x: auto; margin: 1.5rem 0; letter-spacing: -0.2px; }

/* ---------- Steps ---------- */
ol.steps { list-style: none; counter-reset: step; padding: 0; margin: 1.5rem 0; }
ol.steps > li { counter-increment: step; position: relative; padding: .25rem 0 1.1rem 3rem; }
ol.steps > li::before { content: counter(step); position: absolute; left: 0; top: 0;
  width: 1.9rem; height: 1.9rem; background: var(--primary); color: #fff; border-radius: var(--radius-sm);
  font-family: var(--font-mono); font-weight: 500; display: grid; place-items: center; font-size: .85rem; }
ol.steps > li:not(:last-child)::after { content: ""; position: absolute; left: .92rem; top: 2.05rem; bottom: 0; width: 1px; background: var(--line); }
ol.steps > li b { color: var(--ink-strong); }

/* ---------- Deep-dive (expandable) ---------- */
details.deep-dive { border: 1px solid var(--line-strong); border-radius: var(--radius);
  background: var(--bg); margin: 1.5rem 0; overflow: hidden; }
details.deep-dive > summary { cursor: pointer; padding: .85rem 1.1rem; font-weight: 600; color: var(--ink-strong);
  background: var(--bg-soft); list-style: none; display: flex; align-items: center; gap: .5rem; }
details.deep-dive > summary::-webkit-details-marker { display: none; }
details.deep-dive > summary::before { content: "▸"; color: var(--primary); transition: transform .15s; }
details.deep-dive[open] > summary::before { transform: rotate(90deg); }
details.deep-dive > summary .tag { margin-left: auto; font-family: var(--font-mono); font-size: .62rem; font-weight: 500;
  text-transform: uppercase; letter-spacing: .06em; color: var(--primary); background: var(--primary-soft); padding: .12rem .5rem; border-radius: var(--radius-sm); }
details.deep-dive > div { padding: .25rem 1.2rem 1rem; }

/* ---------- Tabs ---------- */
.tabs { margin: 1.5rem 0; }
.tab-list { display: flex; flex-wrap: wrap; gap: .25rem; border-bottom: 1px solid var(--line); }
.tab { background: none; border: 0; padding: .55rem .9rem; font: inherit; font-family: var(--font-mono); font-weight: 500; font-size: .78rem;
  text-transform: uppercase; letter-spacing: .04em; color: var(--ink-soft); cursor: pointer; border-bottom: 2px solid transparent; margin-bottom: -1px; }
.tab:hover { color: var(--ink-strong); }
.tab.is-active { color: var(--primary-dark); border-bottom-color: var(--primary); }
.tab-panel { display: none; padding: 1.1rem .1rem; }
.tab-panel.is-active { display: block; animation: fade .2s var(--ease); }
@keyframes fade { from { opacity: 0; transform: translateY(4px);} to {opacity:1; transform:none;} }

/* ---------- Quiz engine ---------- */
.quiz { border: 1px solid var(--line); border-radius: var(--radius); background: var(--bg-soft);
  padding: 1.25rem 1.35rem; margin: 2rem 0; }
.quiz__head { display: flex; align-items: center; gap: .5rem; font-weight: 600; color: var(--ink-strong);
  font-size: 1.05rem; margin-bottom: .35rem; letter-spacing: -0.3px; }
.quiz__head .ico { font-size: 1.2rem; }
.quiz__score { margin-left: auto; font-family: var(--font-mono); font-size: .8rem; color: var(--ink-soft); font-weight: 500; letter-spacing: -0.2px; }
.quiz__item { padding: 1rem 0; border-top: 1px solid var(--line); }
.quiz__item:first-of-type { border-top: 0; }
.quiz__q { font-weight: 600; color: var(--ink-strong); margin: 0 0 .7rem; letter-spacing: -0.2px; }
.quiz__opts { list-style: none; margin: 0; padding: 0; display: grid; gap: .5rem; }
.quiz__opt { width: 100%; text-align: left; font: inherit; font-size: .95rem; cursor: pointer;
  background: var(--bg); border: 1px solid var(--line); border-radius: var(--radius-sm);
  padding: .65rem .85rem; color: var(--ink); transition: border-color .12s, background .12s; display: flex; gap: .6rem; align-items: center; }
.quiz__opt:hover:not(:disabled) { border-color: var(--primary); background: var(--primary-soft); }
.quiz__opt .mark { width: 1.25rem; flex: 0 0 1.25rem; font-weight: 700; font-family: var(--font-mono); }
.quiz__opt.correct   { border-color: var(--ok);  background: var(--example-soft); color: var(--ok); }
.quiz__opt.incorrect { border-color: var(--bad); background: var(--pitfall-soft); color: var(--bad); }
.quiz__opt:disabled { cursor: default; }
.quiz__exp { margin: .8rem 0 0; padding: .7rem .9rem; border-radius: var(--radius-sm);
  background: var(--info-soft); border: 1px solid var(--line); border-left: 3px solid var(--primary); font-size: .9rem; color: var(--slate); }
.quiz__exp[hidden] { display: none; }
.quiz__exp b { color: var(--ink-strong); }

/* ---------- Interactive widgets ---------- */
.widget { border: 1px solid var(--line-strong); border-radius: var(--radius); background: var(--bg);
  box-shadow: var(--shadow); margin: 1.75rem 0; overflow: hidden; }
.widget__bar { display: flex; align-items: center; gap: .5rem; padding: .65rem 1rem; background: #14193A;
  border-bottom: 1px solid var(--line); color: #fff; font-family: var(--font-mono); font-weight: 500;
  font-size: .72rem; text-transform: uppercase; letter-spacing: .06em; }
.widget__bar .ico { font-size: 1rem; }
.widget__bar .tag { margin-left: auto; font-size: .6rem; font-weight: 500; text-transform: uppercase;
  letter-spacing: .08em; color: #8fb4f5; }
.widget__body { padding: 1.1rem 1.15rem; }
.controls { display: grid; gap: .9rem; margin: .25rem 0 1rem; }
.control { display: grid; grid-template-columns: 150px 1fr auto; align-items: center; gap: .75rem; }
.control label { font-size: .86rem; font-weight: 500; color: var(--ink); }
.control output { font-family: var(--font-mono); font-weight: 500; color: var(--primary-dark); min-width: 4ch; text-align: right; letter-spacing: -0.2px; }
.control select, .control input[type="number"], .control input[type="text"] { font: inherit; font-size: .9rem; padding: .4rem .55rem; border: 1px solid var(--line-strong);
  border-radius: var(--radius-sm); background: var(--bg); color: var(--ink); }
input[type="range"] { -webkit-appearance: none; appearance: none; height: 4px; border-radius: 999px; background: var(--bg-sunken); outline: none; }
input[type="range"]::-webkit-slider-thumb { -webkit-appearance: none; width: 16px; height: 16px; border-radius: 50%;
  background: var(--primary); cursor: pointer; border: 3px solid #fff; box-shadow: var(--shadow-sm); }
input[type="range"]::-moz-range-thumb { width: 16px; height: 16px; border-radius: 50%; background: var(--primary); cursor: pointer; border: 3px solid #fff; }
.btn { display: inline-flex; align-items: center; justify-content: center; gap: .45rem; font-family: var(--font-mono); font-weight: 500;
  font-size: .76rem; text-transform: uppercase; letter-spacing: .05em; cursor: pointer; border: 1px solid var(--primary);
  background: var(--primary); color: #fff; padding: .5rem .9rem; border-radius: var(--radius-sm); transition: background .12s, color .12s, border-color .12s; }
.btn:hover { background: var(--primary-dark); border-color: var(--primary-dark); }
.btn--ghost { background: transparent; color: var(--primary); }
.btn--ghost:hover { background: var(--primary-soft); color: var(--primary-dark); }
.readout { font-family: var(--font-mono); font-size: .9rem; letter-spacing: -0.2px; }
.verdict { font-family: var(--font-mono); font-weight: 500; padding: .15rem .6rem; border-radius: var(--radius-sm); text-transform: uppercase; letter-spacing: .04em; font-size: .82rem; }
.verdict.pass { background: var(--example-soft); color: var(--ok); border: 1px solid var(--ok); }
.verdict.fail { background: var(--pitfall-soft); color: var(--bad); border: 1px solid var(--bad); }

/* ---------- Module footer nav ---------- */
.module-footer { display: flex; gap: 1rem; margin-top: 3.5rem; padding-top: 1.5rem; border-top: 1px solid var(--line); }
.module-footer a { flex: 1; display: block; border: 1px solid var(--line); border-radius: var(--radius);
  padding: .9rem 1.1rem; color: var(--ink); background: var(--bg); box-shadow: var(--shadow-sm); transition: border-color .12s; }
.module-footer a:hover { border-color: var(--primary); text-decoration: none; }
.module-footer .dir { font-size: .66rem; color: var(--ink-soft); text-transform: uppercase; letter-spacing: .08em; font-weight: 500; }
.module-footer .ttl { font-weight: 600; color: var(--ink-strong); letter-spacing: -0.2px; }
.module-footer .next { text-align: right; }

/* ---------- Utilities ---------- */
.muted { color: var(--ink-soft); }
.small { font-size: .85rem; }
.center { text-align: center; }
.nowrap { white-space: nowrap; }
.mono { font-family: var(--font-mono); letter-spacing: -0.2px; }
.scrim { display: none; }

/* ============================================================================
   Diagrams, mind maps & "show, don't tell" primitives
   ========================================================================== */
.mindmap { margin: 1.75rem 0; }
.mindmap svg { width: 100%; height: auto; display: block; }
.mm-center      { font-family: var(--font-sans); font-weight: 600; font-size: 18px; fill: #fff; letter-spacing: -0.4px; }
.mm-center-sub  { font-family: var(--font-mono); font-weight: 500; font-size: 10.5px; fill: #9fc0f7; letter-spacing: 0; }
.mm-title       { font-family: var(--font-sans); font-weight: 600; font-size: 15px; fill: #14193A; letter-spacing: -0.3px; }
.mm-item        { font-family: var(--font-sans); font-weight: 400; font-size: 13px; fill: #4F5670; }
.mm-cap, .figure__caption.mm-cap { text-align: center; color: var(--ink-soft); font-size: .82rem; margin-top: .55rem; }

.legend { display: flex; flex-wrap: wrap; gap: .5rem 1.15rem; justify-content: center; margin: .8rem 0 0; }
.legend .k { display: inline-flex; align-items: center; gap: .42rem; font-size: .8rem; color: var(--ink); }
.legend .sw { width: 14px; height: 14px; border-radius: 2px; flex: 0 0 14px; border: 1px solid rgba(26,32,64,.14); }

.diagram-grid { display: grid; grid-template-columns: repeat(auto-fit, minmax(260px, 1fr)); gap: 1rem; margin: 1.5rem 0; align-items: start; }

.figure--hero .figure__frame { background: linear-gradient(180deg, var(--bg), var(--bg-soft)); border-color: var(--line-strong); }

.vs { display: grid; grid-template-columns: 1fr auto 1fr; gap: 1rem; align-items: stretch; margin: 1.5rem 0; }
.vs .side { border: 1px solid var(--line); border-radius: var(--radius); padding: 1rem 1.1rem; background: var(--bg-soft); }
.vs .side h4 { margin: 0 0 .5rem; color: var(--ink-strong); letter-spacing: -0.3px; }
.vs .side ul { margin: 0; padding-left: 1.1rem; font-size: .92rem; }
.vs .mid { display: grid; place-items: center; font-family: var(--font-mono); font-weight: 500; color: var(--ink-faint); font-size: .95rem; text-transform: uppercase; }
@media (max-width: 600px) { .vs { grid-template-columns: 1fr; } .vs .mid { padding: .15rem; } }

.flowline { display: flex; flex-wrap: wrap; align-items: stretch; gap: .4rem; margin: 1.5rem 0; }
.flowline .node { flex: 1 1 0; min-width: 110px; border: 1px solid var(--line); border-radius: var(--radius-sm);
  background: var(--bg); padding: .6rem .7rem; text-align: center; box-shadow: var(--shadow-sm); }
.flowline .node b { display: block; color: var(--ink-strong); font-size: .9rem; letter-spacing: -0.2px; }
.flowline .node span { font-size: .74rem; color: var(--ink-soft); }
.flowline .arrow { display: grid; place-items: center; color: var(--primary); font-weight: 700; flex: 0 0 auto; }
@media (max-width: 600px) { .flowline { flex-direction: column; } .flowline .arrow { transform: rotate(90deg); } }

/* ---------- Responsive ---------- */
@media (max-width: 920px) {
  .sidebar { position: fixed; left: 0; top: 0; transform: translateX(-100%); transition: transform .25s var(--ease); box-shadow: var(--shadow-lg); }
  .sidebar.is-open { transform: translateX(0); }
  .menu-btn { display: inline-grid; place-items: center; }
  .scrim.is-open { display: block; position: fixed; inset: 0; background: rgba(26,32,64,.4); z-index: 25; }
  .module-main { padding: 1.75rem 1.15rem 4rem; }
  .module-main h1 { font-size: 1.95rem; }
  .control { grid-template-columns: 1fr; gap: .35rem; }
  .control output { text-align: left; }
  .module-footer { flex-direction: column; }
}

/* ---------- Print ---------- */
@media print {
  .sidebar, .topbar, .module-footer, .menu-btn { display: none !important; }
  .module-main { max-width: none; }
  .widget, .quiz, .figure { break-inside: avoid; }
}

/* ============================================================================
   Dark theme — toggled via [data-theme="dark"] on <html> (mirrors @vinxi/design
   .theme-dark). Diagram/widget surfaces stay light "islands" so the hand-authored
   SVG diagrams remain crisp on the dark page.
   ========================================================================== */
:root[data-theme="dark"] {
  --bg:#0B1020; --bg-soft:#141A30; --bg-sunken:#1C2238;
  --ink:#E8EBF2; --ink-strong:#F4F6FB; --ink-soft:#8B92AB; --ink-faint:#6A718A;
  --slate:#C2C8DA; --graphite:#A8AEC4;
  --line:#232A48; --line-strong:#313A60; --fog:#1C2238;
  --primary:#4D8DFF; --primary-dark:#6BA0FF; --primary-soft:rgba(77,141,255,.16);
  --accent:#4D8DFF; --accent-soft:rgba(77,141,255,.16);
  --key:#6BA0FF; --key-soft:rgba(77,141,255,.13);
  --info:#4D8DFF; --info-soft:rgba(77,141,255,.11);
  --pitfall:#FF6B62; --pitfall-soft:rgba(255,107,98,.13);
  --example:#4FBE85; --example-soft:rgba(79,190,133,.15);
  --analogy:#FFC04D; --analogy-soft:rgba(255,192,77,.15);
  --numbers:#9FB6E6; --numbers-soft:#141A30;
  --ok:#4FBE85; --bad:#FF6B62;
  --shadow:0 1px 2px rgba(0,0,0,.32), 0 4px 12px rgba(0,0,0,.36);
  --shadow-sm:0 1px 2px rgba(0,0,0,.34);
  --shadow-lg:0 16px 32px rgba(0,0,0,.5);
}
:root[data-theme="dark"] .topbar { background: rgba(11,16,32,.85); }

/* light "islands" — keep diagram/widget surfaces light so authored SVGs read */
:root[data-theme="dark"] .figure__frame,
:root[data-theme="dark"] .widget__body,
:root[data-theme="dark"] .diagram-grid {
  --bg:#FBFDFF; --bg-soft:#F2F5F9; --bg-sunken:#E9EEF5;
  --ink:#1A2040; --ink-strong:#14193A; --ink-soft:#6B7280; --ink-faint:#8E94A6;
  --slate:#3D4566; --graphite:#4F5670; --line:#DFE3EA; --line-strong:#C9D0DB; --fog:#E4ECF5;
  --primary:#0066E3; --primary-dark:#0055C0; --primary-soft:#E8F0FE; --accent:#0066E3; --accent-soft:#E8F0FE;
  --key:#0055C0; --key-soft:#E8F0FE; --info:#0066E3; --info-soft:#EEF4FE; --pitfall:#C8362F; --pitfall-soft:#FBECEB;
  --example:#1F8855; --example-soft:#E8F5EE; --analogy:#B57E00; --analogy-soft:#FCF3DF; --numbers:#1A2040; --numbers-soft:#F2F5F9;
  --ok:#1F8855; --bad:#C8362F;
  background:#FBFDFF; color:#1A2040;
}
:root[data-theme="dark"] .figure--hero .figure__frame { background:#FBFDFF; }
:root[data-theme="dark"] .figure__caption { color: var(--ink-soft); }

/* theme toggle (injected into the topbar by course.js) */
.theme-toggle { width:34px; height:34px; flex:0 0 auto; display:grid; place-items:center;
  border:1px solid var(--line); border-radius:var(--radius-sm); background:var(--bg); color:var(--ink-soft);
  cursor:pointer; font-size:1rem; line-height:1; transition:border-color .12s, color .12s; }
.theme-toggle:hover { border-color:var(--primary); color:var(--primary); }