/* Models of Computation - shared stylesheet. All design lives here; pages carry no styles of their own. */
/* ============================= TOKENS ============================= */
:root{
  color-scheme:light;
  --bg:#eff1ee;
  --surface:#ffffff;
  --surface-2:#e6e9e2;
  --surface-3:#dde1d8;
  --ink:#171b2a;
  --ink-soft:#4b5163;
  --ink-faint:#7b8092;
  --line:#d6dbd0;
  --line-strong:#b9c0b2;
  --true:#146b5c;
  --true-bg:#dcece7;
  --false:#9a3324;
  --false-bg:#f1ded9;
  --gold:#8f6714;
  --gold-bg:#efe4c8;
  --shadow: 0 1px 2px rgba(23,27,42,.06), 0 8px 24px -12px rgba(23,27,42,.18);
  --radius-s:4px;
  --radius-m:8px;
  --font-display:'Fraunces', ui-serif, Georgia, serif;
  --font-body:'Source Serif 4', ui-serif, Georgia, serif;
  --font-mono:'JetBrains Mono', ui-monospace, 'SF Mono', Menlo, monospace;
}
@media (prefers-color-scheme: dark){
  :root:not([data-theme="light"]){
    color-scheme:dark;
    --bg:#12141d; --surface:#181b27; --surface-2:#1f2330; --surface-3:#282c3b;
    --ink:#e9eaf0; --ink-soft:#aeb3c6; --ink-faint:#7b8098;
    --line:#2c3040; --line-strong:#3a3f52;
    --true:#4ec7ab; --true-bg:#193631;
    --false:#e58269; --false-bg:#3a2420;
    --gold:#dcaa4d; --gold-bg:#3a2f18;
    --shadow: 0 1px 2px rgba(0,0,0,.3), 0 12px 32px -16px rgba(0,0,0,.6);
  }
}
:root[data-theme="dark"]{
  color-scheme:dark;
  --bg:#12141d; --surface:#181b27; --surface-2:#1f2330; --surface-3:#282c3b;
  --ink:#e9eaf0; --ink-soft:#aeb3c6; --ink-faint:#7b8098;
  --line:#2c3040; --line-strong:#3a3f52;
  --true:#4ec7ab; --true-bg:#193631;
  --false:#e58269; --false-bg:#3a2420;
  --gold:#dcaa4d; --gold-bg:#3a2f18;
  --shadow: 0 1px 2px rgba(0,0,0,.3), 0 12px 32px -16px rgba(0,0,0,.6);
}

/* ============================= RESET / BASE ============================= */
*,*::before,*::after{box-sizing:border-box}
body{
  margin:0; background:var(--bg); color:var(--ink); font-family:var(--font-body);
  font-size:16.5px; line-height:1.65; -webkit-font-smoothing:antialiased;
}
::selection{ background:var(--gold-bg); color:var(--ink); }
a{ color:inherit; }
:focus-visible{ outline:2px solid var(--gold); outline-offset:2px; border-radius:2px; }
@media (prefers-reduced-motion: reduce){ *{ animation-duration:.001ms !important; transition-duration:.001ms !important; } }

/* ============================= APP SHELL ============================= */
.app{ display:flex; min-height:100vh; }

.sidebar{
  width:296px; flex:0 0 296px; height:100vh; position:sticky; top:0; overflow-y:auto;
  background:var(--surface-2); border-right:1px solid var(--line);
  display:flex; flex-direction:column; scrollbar-width:thin;
}
.sidebar-head{ padding:26px 24px 18px; border-bottom:1px solid var(--line); }
.brand-mark{
  display:inline-flex; align-items:center; justify-content:center;
  width:34px; height:34px; border-radius:50%; border:2px solid var(--ink); position:relative; margin-bottom:14px;
}
.brand-mark::after{ content:""; width:22px; height:22px; border-radius:50%; border:1.4px solid var(--ink); }
.brand-code{
  font-family:var(--font-mono); font-size:11.5px; letter-spacing:.14em;
  color:var(--ink-faint); text-transform:uppercase; display:block; margin-bottom:4px;
}
.brand-title a{ color:inherit; text-decoration:none; }
.brand-title{ font-family:var(--font-display); font-weight:700; font-size:20px; line-height:1.15; color:var(--ink); text-wrap:balance; }
.brand-sub{ font-size:12.5px; color:var(--ink-soft); margin-top:6px; line-height:1.5; }
.theme-toggle{ margin-top:16px; display:inline-flex; gap:2px; padding:3px; background:var(--surface); border:1px solid var(--line); border-radius:20px; }
.theme-toggle button{
  border:none; background:transparent; color:var(--ink-faint); font-family:var(--font-mono);
  font-size:10.5px; letter-spacing:.06em; padding:5px 10px; border-radius:16px; cursor:pointer;
}
.theme-toggle button.active{ background:var(--ink); color:var(--bg); }

.nav-scroll{ flex:1; padding:10px 12px 32px; }
.nav-group{ margin-top:4px; }
.nav-group-head{ display:flex; align-items:stretch; border-radius:var(--radius-s); }
.nav-group-head:hover{ background:var(--surface-3); }
.nav-group-btn{
  flex:1 1 auto; display:flex; align-items:center; gap:10px; text-decoration:none;
  padding:10px 12px; font-family:var(--font-mono); font-size:11px;
  letter-spacing:.09em; text-transform:uppercase; color:var(--ink-soft);
}
.nav-group-head:hover .nav-group-btn, .nav-group.active>.nav-group-head .nav-group-btn{ color:var(--ink); }
.chev-btn{ background:transparent; border:none; cursor:pointer; color:var(--ink-faint); padding:0 12px; display:flex; align-items:center; }
.chev-btn .chev{ display:inline-block; font-size:9px; transition:transform .15s ease; }
.nav-group.open .chev-btn .chev{ transform:rotate(90deg); }
.nav-group-num{
  width:20px; height:20px; border-radius:50%; flex:0 0 20px; display:inline-flex; align-items:center;
  justify-content:center; font-size:10px; border:1.3px solid var(--ink-faint); color:var(--ink-faint);
}
.nav-group.active .nav-group-num{ border-color:var(--gold); color:var(--gold); }
.nav-list{ list-style:none; margin:2px 0 8px; padding:0 0 0 30px; display:none; }
.nav-group.open .nav-list{ display:block; }
.nav-list li a{
  display:block; text-decoration:none; color:var(--ink-soft); font-size:13.5px; line-height:1.4;
  padding:6px 10px 6px 12px; border-left:1.5px solid var(--line); margin-left:1px;
}
.nav-list li a:hover{ color:var(--ink); border-left-color:var(--ink-faint); }
.nav-list li a.active{ color:var(--gold); border-left-color:var(--gold); font-weight:600; }

.main{ flex:1 1 auto; min-width:0; }

.page-hero{ padding:64px 56px 40px; max-width:1040px; border-bottom:1px solid var(--line); }
.eyebrow{
  font-family:var(--font-mono); font-size:12px; letter-spacing:.14em; text-transform:uppercase;
  color:var(--ink-faint); display:flex; align-items:center; gap:10px; margin-bottom:18px;
}
.eyebrow .dot{ width:7px; height:7px; border-radius:50%; background:var(--gold); flex:0 0 auto; }
.page-title{
  font-family:var(--font-display); font-weight:700; font-size:clamp(34px,5vw,54px);
  line-height:1.04; text-wrap:balance; margin:0 0 20px; letter-spacing:-.01em;
}
.page-dek{ font-size:18.5px; line-height:1.6; color:var(--ink-soft); max-width:66ch; text-wrap:pretty; }
.page-body{ padding:8px 56px 40px; max-width:1040px; }

.section{ padding:56px 0; border-bottom:1px solid var(--line); }
.section:last-child{ border-bottom:none; }
.section-kicker{ font-family:var(--font-mono); font-size:12.5px; color:var(--gold); letter-spacing:.05em; margin-bottom:8px; }
.section h2{ font-family:var(--font-display); font-weight:700; font-size:30px; line-height:1.2; margin:0 0 22px; text-wrap:balance; scroll-margin-top:24px; }
.section h3{ font-family:var(--font-display); font-weight:600; font-size:21px; margin:34px 0 14px; scroll-margin-top:24px; }
.section p{ margin:0 0 18px; max-width:70ch; }
.section p.wide{ max-width:none; }
.section ul, .section ol{ margin:0 0 18px; padding-left:1.3em; max-width:70ch; }
.section li{ margin-bottom:8px; }
.section strong{ font-weight:600; color:var(--ink); }
.section em{ font-style:italic; }

.box{ border:1px solid var(--line-strong); border-radius:var(--radius-m); background:var(--surface); padding:22px 26px; margin:24px 0; }
.box-label{ font-family:var(--font-mono); font-size:10.5px; letter-spacing:.12em; text-transform:uppercase; display:inline-flex; align-items:center; gap:7px; margin-bottom:12px; font-weight:600; }
.box.definition{ border-left:3px solid var(--ink); }
.box.definition .box-label{ color:var(--ink-soft); }
.box.theorem{ border-left:3px solid var(--gold); background:linear-gradient(180deg,var(--gold-bg),var(--surface) 60px); }
.box.theorem .box-label{ color:var(--gold); }
.box.intuition{ border:1px dashed var(--line-strong); background:transparent; box-shadow:none; }
.box.intuition .box-label{ color:var(--ink-faint); }
.box.example{ border-left:3px solid var(--ink-faint); }
.box.example .box-label{ color:var(--ink-faint); }
.box.warning{ border-left:3px solid var(--false); background:linear-gradient(180deg,var(--false-bg),var(--surface) 70px); }
.box.warning .box-label{ color:var(--false); }
.box p:last-child, .box ul:last-child, .box ol:last-child{ margin-bottom:0; }
.box .math-block{ margin:14px 0; }

.tag{ display:inline-flex; align-items:center; gap:5px; font-family:var(--font-mono); font-size:11px; padding:3px 9px; border-radius:20px; letter-spacing:.03em; }
.tag.true{ background:var(--true-bg); color:var(--true); }
.tag.false{ background:var(--false-bg); color:var(--false); }
.tag.neutral{ background:var(--surface-3); color:var(--ink-soft); }

.table-wrap{ overflow-x:auto; margin:22px 0; border:1px solid var(--line); border-radius:var(--radius-m); }
table{ border-collapse:collapse; width:100%; font-size:14.5px; background:var(--surface); }
table caption{ text-align:left; padding:12px 16px 0; font-family:var(--font-mono); font-size:11.5px; color:var(--ink-faint); }
th,td{ padding:9px 15px; text-align:center; vertical-align:top; border-bottom:1px solid var(--line); font-variant-numeric:tabular-nums; }
th{ background:var(--surface-2); font-family:var(--font-mono); font-weight:600; font-size:12.5px; color:var(--ink-soft); }
tr:last-child td{ border-bottom:none; }
tr:hover td{ background:var(--surface-2); }

.derivation{ margin:22px 0; border-left:2px solid var(--line-strong); padding-left:22px; }
.dstep{ position:relative; padding:9px 0; }
.dstep::before{ content:""; position:absolute; left:-27px; top:16px; width:9px; height:9px; border-radius:50%; background:var(--surface); border:1.5px solid var(--ink-faint); }
.dstep .drule{ float:right; font-family:var(--font-mono); font-size:11.5px; color:var(--ink-faint); padding-left:14px; }
.dstep .dnum{ font-family:var(--font-mono); font-size:12px; color:var(--gold); margin-right:10px; }


figure.diagram{ margin:28px 0; }
figure.diagram > svg{ width:100%; height:auto; display:block; background:var(--surface); border:1px solid var(--line); border-radius:var(--radius-m); }
figure.diagram figcaption{ font-size:13px; color:var(--ink-faint); margin-top:10px; text-align:center; }
svg text{ font-family:var(--font-mono); fill:currentColor; }

.grid-2{ display:grid; grid-template-columns:1fr 1fr; gap:22px; margin:24px 0; }
@media (max-width:760px){ .grid-2{ grid-template-columns:1fr; } }

.panel{ border:1px solid var(--line-strong); border-radius:var(--radius-m); background:var(--surface); padding:26px 28px; margin:28px 0; box-shadow:var(--shadow); }
.panel-head{ display:flex; align-items:center; justify-content:space-between; gap:16px; margin-bottom:18px; flex-wrap:wrap; }
.panel-title{ font-family:var(--font-display); font-weight:700; font-size:19px; }
.btnrow{ display:flex; gap:8px; flex-wrap:wrap; }
button.step-btn{
  font-family:var(--font-mono); font-size:12px; letter-spacing:.03em; padding:8px 14px; border-radius:20px;
  border:1px solid var(--line-strong); background:var(--surface); color:var(--ink); cursor:pointer;
  transition:background .12s ease, color .12s ease, border-color .12s ease;
}
button.step-btn:hover{ background:var(--surface-2); }
button.step-btn.primary{ background:var(--ink); color:var(--bg); border-color:var(--ink); }
button.step-btn:disabled{ opacity:.4; cursor:not-allowed; }
.narration{ font-size:14.5px; color:var(--ink-soft); border-top:1px solid var(--line); margin-top:18px; padding-top:14px; min-height:44px; }
.narration strong{ color:var(--ink); }

code{ font-family:var(--font-mono); font-size:.92em; background:var(--surface-2); padding:1px 6px; border-radius:4px; }

mjx-container{ font-size:1em !important; }
.math-block{ overflow-x:auto; padding:4px 0; }
.math-block mjx-container{ margin:0 auto !important; }

.pager{ display:flex; justify-content:space-between; gap:16px; padding:36px 56px 90px; border-top:1px solid var(--line); max-width:1040px; }
.pager a{ text-decoration:none; }
.pager-card{ border:1px solid var(--line-strong); border-radius:var(--radius-m); padding:16px 20px; background:var(--surface); max-width:320px; }
.pager-card .eyebrow{ margin-bottom:6px; }
.pager-card .ptitle{ font-family:var(--font-display); font-weight:600; font-size:16px; }
.pager-next{ text-align:right; margin-left:auto; }

.mobile-bar{ display:none; }
@media (max-width:900px){
  .sidebar{ position:fixed; inset:0 auto 0 0; z-index:40; transform:translateX(-100%); transition:transform .2s ease; box-shadow:var(--shadow); }
  .sidebar.open{ transform:translateX(0); }
  .mobile-bar{ display:flex; align-items:center; gap:12px; position:sticky; top:0; z-index:30; background:var(--surface); border-bottom:1px solid var(--line); padding:14px 18px; }
  .mobile-bar strong{ font-family:var(--font-mono); font-size:12px; letter-spacing:.06em; }
  .mobile-bar button{ background:none; border:1px solid var(--line-strong); border-radius:8px; padding:7px 10px; font-family:var(--font-mono); font-size:12px; }
  .page-hero, .page-body, .pager{ padding-left:24px; padding-right:24px; }
  .grid-2{ grid-template-columns:1fr; }
}
/* ============================= PAGE-SPECIFIC ============================= */
.pm-cell{ background:var(--surface-2); border:1px solid var(--line-strong); border-radius:6px; text-align:center; padding:10px 0; }
.pm-cell.never{ background:transparent; border:1px dashed var(--false); color:var(--false); }
.ss-grid{ display:grid; grid-template-columns:230px 1fr; gap:24px; align-items:start; }
@media (max-width:760px){ .ss-grid{ grid-template-columns:1fr; } }
.ss-hidden{ opacity:0; }
.tp-reveal{ display:none; }
.tp-reveal.shown{ display:block; }

details.quiz{ border:1px dashed var(--line-strong); border-radius:var(--radius-m); padding:16px 26px; margin:24px 0; }
details.quiz summary{ cursor:pointer; list-style:none; display:flex; align-items:baseline; gap:14px; }
details.quiz summary::-webkit-details-marker{ display:none; }
details.quiz summary .box-label{ margin-bottom:0; color:var(--ink-faint); flex:0 0 auto; }
details.quiz summary::after{ content:"show answer"; margin-left:auto; padding-left:14px; font-family:var(--font-mono); font-size:10.5px; letter-spacing:.08em; text-transform:uppercase; color:var(--gold); flex:0 0 auto; white-space:nowrap; }
details.quiz[open] summary::after{ content:"hide answer"; }
details.quiz .answer{ margin-top:14px; padding-top:14px; border-top:1px dashed var(--line); }
details.quiz .answer p:last-child{ margin-bottom:0; }
/* Smooth in-page scrolling is switched on by nav.js only after MathJax has finished,
   so the initial jump to a #hash is never cancelled by the reflow. */
@media (prefers-reduced-motion: no-preference){ html.ready{ scroll-behavior:smooth; } }