/* d0 OS showcase. Built on /d0-tokens.css (night and paper themes) and the journey's chapter pattern:
   a monochrome editorial surface where colour belongs to the figures, hairline strokes, one amber accent.
   Newsreader for headlines, IBM Plex Mono for figures and labels. Static HTML stays readable without JS. */
:root{--header:96px;--pad:clamp(16px,5.5vw,88px);--sans:Arial,Helvetica,sans-serif;--amber:var(--accent-warm);--hair:rgba(244,242,236,.14)}
*{box-sizing:border-box}
html{scroll-behavior:smooth;scroll-padding-top:104px;-webkit-text-size-adjust:100%;text-size-adjust:100%}
body{margin:0;background:var(--surface);color:var(--ink);font:16px/1.7 var(--font-mono)}
h1,h2,h3,p,dl,dd,figure{margin:0}
h1,h2,h3{font-family:var(--font-serif);font-weight:400;line-height:1.08;letter-spacing:-.03em;text-wrap:balance}
a{color:inherit;text-decoration:none}
img{display:block;max-width:100%;height:auto}
button,summary{font:inherit;color:inherit}
:focus-visible{outline:2px solid var(--amber);outline-offset:4px}
[hidden]{display:none!important}
.skip-link{position:fixed;z-index:60;left:16px;top:10px;padding:12px 16px;background:var(--ink);color:var(--surface);transform:translateY(-180%)}
.skip-link:focus{transform:none}
.eyebrow{font:500 11.7px/1.6 var(--font-mono);letter-spacing:.16em;color:var(--ink-muted)}

/* Reading progress and the floating header. */
.reading-progress{position:fixed;z-index:40;inset:0 0 auto;height:2px;background:rgba(244,242,236,.08)}
.reading-progress span{display:block;height:100%;background:var(--amber);transform:scaleX(0);transform-origin:left}
.site-header{position:fixed;z-index:30;top:14px;left:50%;transform:translateX(-50%);width:calc(100% - 32px);max-width:1480px;height:66px;display:flex;align-items:center;gap:6px;padding:9px 10px 9px 18px;background:rgba(20,20,20,.93);border:1px solid rgba(255,255,255,.14);border-radius:18px;-webkit-backdrop-filter:blur(20px);backdrop-filter:blur(20px);transition:transform .24s ease}
.site-header.retracted{transform:translate(-50%,-120px)}
.site-header.retracted:focus-within{transform:translateX(-50%)}
.brand{display:inline-flex;align-items:center;gap:11px;min-height:44px;margin-right:auto;white-space:nowrap}
.brand img{width:30px;height:30px}
.brand>span{font:27px/.95 var(--font-serif);letter-spacing:-.05em}
.brand-sub{display:block;margin-top:5px;font:9.5px/1.5 var(--font-mono);letter-spacing:.06em;text-transform:uppercase;color:#a5a5a5}
.site-nav{display:flex;align-items:center;gap:2px}
.site-nav a,.site-menu-panel a{display:inline-flex;align-items:center;min-height:44px;padding:10px 13px;border-radius:10px;font:500 13px/1.3 var(--sans);color:#c9c9c4;white-space:nowrap}
.site-nav a:hover,.site-menu-panel a:hover{background:rgba(255,255,255,.07);color:#fff}
.motion-toggle{display:inline-flex;align-items:center;gap:9px;min-height:44px;min-width:44px;margin-left:8px;padding:10px 14px;border:1px solid rgba(255,255,255,.2);border-radius:10px;background:none;cursor:pointer;font:12px/1.2 var(--font-mono);letter-spacing:.04em;color:#dedcd6}
.motion-toggle:hover{background:rgba(255,255,255,.07)}
.motion-icon{width:10px;height:12px;border-left:3px solid currentColor;border-right:3px solid currentColor}
.motion-toggle[aria-pressed=true] .motion-icon{width:0;height:0;border:6px solid transparent;border-left:10px solid currentColor;border-right:0;margin-left:2px}
#motion-state{color:var(--amber)}
.site-menu{display:none;position:relative}
.site-menu>summary{list-style:none;display:inline-flex;align-items:center;min-height:44px;padding:10px 14px;border:1px solid rgba(255,255,255,.2);border-radius:10px;cursor:pointer;font:500 13px/1.2 var(--sans)}
.site-menu>summary::-webkit-details-marker{display:none}
.site-menu-panel{position:absolute;right:0;top:calc(100% + 12px);display:flex;flex-direction:column;min-width:220px;padding:8px;background:#151515;border:1px solid rgba(255,255,255,.16);border-radius:14px;box-shadow:0 20px 60px rgba(0,0,0,.5)}

/* Chapters: copy and figure side by side, alternating; the figure stays in view beside a long list. */
main{display:block}
.chapter{position:relative;display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:clamp(36px,5vw,88px);align-items:start;max-width:1480px;margin:0 auto;padding:120px var(--pad);border-bottom:1px solid var(--hair)}
.chapter.reverse .chapter-copy{order:2}
.chapter.reverse .chapter-visual{order:1}
.chapter-copy{min-width:0;max-width:640px}
.chapter.reverse .chapter-copy{justify-self:end}
.chapter .eyebrow{margin-bottom:22px}
.chapter h1{font-size:clamp(56px,6vw,98px);letter-spacing:-.04em}
.chapter h2{font-size:clamp(44px,4.4vw,74px)}
.chapter h1 span,.chapter h2 span{display:block}
.chapter h1 span:last-child,.chapter h2 span:last-child{font-style:italic;color:#d6d4ce}
.chapter-body{margin-top:28px;font:17px/1.75 var(--sans);color:var(--ink-muted)}
.chapter-body p+p{margin-top:16px}
.chapter-equation{margin:26px 0 0;padding-left:18px;border-left:1px solid var(--amber);font:13.5px/1.9 var(--font-mono);white-space:pre-wrap;overflow-wrap:anywhere;color:var(--amber)}
.chapter-bridge{margin-top:34px;padding-top:20px;border-top:1px solid var(--line);font:13px/1.9 var(--font-mono);color:#a9a8a2}
.chapter-visual{position:sticky;top:calc(var(--header) + 12px);align-self:start;min-width:0;padding-top:26px;border-top:1px solid rgba(244,242,236,.24)}
.chapter-visual::after{content:'';position:absolute;left:0;top:-1px;width:55px;height:2px;background:var(--amber)}
.visual-label{font:29px/1.2 var(--font-serif);letter-spacing:-.02em;color:#e0ded8}
.explanation-canvas{display:block;width:100%;aspect-ratio:1.4;height:auto;max-height:440px;margin:12px 0 16px;background:radial-gradient(ellipse at 50% 40%,#1e1e1e 0%,rgba(16,16,16,0) 75%)}
.chapter-visual figcaption{padding-top:18px;border-top:1px solid rgba(244,242,236,.16);font:15px/1.75 var(--sans);color:#c6c4be}
.chapter-visual figcaption span{display:block;margin-top:10px;font:11.5px/1.8 var(--font-mono);letter-spacing:.04em;color:#9d9c96}

/* Hero: the real wallpaper poster under one canvas. */
.hero{align-items:center;min-height:100svh;padding-top:calc(var(--header) + 64px);grid-template-columns:minmax(0,.92fr) minmax(0,1.08fr)}
.hero .chapter-copy{max-width:620px}
.hero-actions{display:flex;flex-wrap:wrap;align-items:center;gap:10px 24px;margin-top:30px}
.solid-link{display:inline-flex;align-items:center;gap:16px;min-height:48px;padding:13px 20px;background:var(--ink);color:#141414;font:500 13px/1.3 var(--sans)}
.solid-link:hover{background:var(--amber)}
.quiet-link{display:inline-flex;align-items:center;gap:12px;min-height:44px;padding:10px 0;border-bottom:1px solid var(--line);font:13px/1.3 var(--sans);color:#dddbd5}
.quiet-link:hover{border-bottom-color:var(--ink)}
.edition-pill{display:flex;flex-wrap:wrap;justify-content:space-between;align-items:center;gap:6px 22px;margin-top:34px;padding:10px 0;border-top:1px solid rgba(244,242,236,.28);border-bottom:1px solid rgba(244,242,236,.28);font:12px/1.6 var(--font-mono);color:var(--ink-muted)}
.edition-pill a{display:inline-flex;align-items:center;gap:8px;min-height:44px;color:var(--ink)}
.edition-pill a:hover{color:var(--amber)}
.hero-visual{position:relative;top:auto}
.hero-screen{position:relative;margin:12px 0 16px;aspect-ratio:1.4;background:#000;overflow:hidden}
.hero-poster,.hero-canvas{position:absolute;inset:0;width:100%;height:100%}
.hero-mark{position:absolute;left:3.5%;bottom:3%;width:auto;height:28%}
.hero-canvas{opacity:0;transition:opacity .6s ease}
.hero-screen[data-state] .hero-canvas{opacity:1}

/* Feature lists. */
.feature-list{list-style:none;margin:30px 0 0;padding:0;border-top:1px solid var(--line)}
.feature-list-more{margin-top:0;border-top:0}
.feature-list li{padding:20px 0 22px;border-bottom:1px solid var(--hair)}
.feature-head{display:flex;flex-wrap:wrap;justify-content:space-between;align-items:baseline;gap:6px 18px}
.feature-list h3{font-size:25px;line-height:1.15;letter-spacing:-.02em;color:var(--ink)}
.feature-list p{margin-top:9px;font:15.5px/1.7 var(--sans);color:var(--ink-muted)}
.feature-list .fact{margin-top:12px;padding-left:12px;border-left:1px solid var(--amber);font:12.5px/1.75 var(--font-mono);color:var(--ink)}
.feature-list .credit{margin-top:8px;font:11.5px/1.7 var(--font-mono);color:#9d9c96}
.status{display:inline-flex;align-items:center;gap:8px;white-space:nowrap;font:11px/1.3 var(--font-mono);letter-spacing:.09em;text-transform:uppercase;color:var(--ink-muted)}
.status::before{content:'';flex:none;width:8px;height:8px;border-radius:50%;background:currentColor}
.status-daily{color:var(--ink)}
.status-test::before{width:6px;height:6px;background:none;border:1.5px solid currentColor}
.status-none::before{width:8px;height:0;border-radius:0;border-top:1.5px solid currentColor;background:none}
.feature-more>summary{list-style:none;display:flex;align-items:center;justify-content:space-between;gap:16px;min-height:52px;padding:12px 0;cursor:pointer;font:12px/1.4 var(--font-mono);letter-spacing:.12em;text-transform:uppercase;color:var(--ink)}
.feature-more>summary::-webkit-details-marker{display:none}
.feature-more>summary:hover{color:var(--amber)}
.more-sign{position:relative;width:14px;height:14px;flex:none}
.more-sign::before,.more-sign::after{content:'';position:absolute;left:0;right:0;top:6px;height:1.5px;background:currentColor}
.more-sign::after{transform:rotate(90deg);transition:transform .2s}
.feature-more[open] .more-sign::after{transform:rotate(0)}
.more-open,.feature-more[open] .more-closed{display:none}
.feature-more[open] .more-open{display:inline}
.feature-more[open]>summary{border-bottom:1px solid var(--hair)}
.wallpaper-pair{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin-top:14px}
.wallpaper-pair figure img{width:100%;aspect-ratio:16/9;object-fit:cover;border:1px solid var(--hair)}
.wallpaper-pair figcaption{margin-top:6px;font:11px/1.5 var(--font-mono);letter-spacing:.08em;text-transform:uppercase;color:var(--ink-soft)}
.wallpaper-pair .asset-note{grid-column:1/-1;margin-top:0;font:11.5px/1.6 var(--font-mono);color:#9d9c96}

/* Paper sections: the numbers band and the status legend. */
.paper-section{background:var(--surface);color:var(--ink)}
.paper-section .eyebrow{color:var(--ink-muted)}
.paper-section h2{font-size:clamp(44px,5vw,78px);margin-top:18px}
.paper-section h2 em{color:var(--ink-muted)}
.paper-link{display:inline-flex;align-items:center;gap:10px;min-height:44px;padding:10px 0;font:14px/1.4 var(--sans);color:var(--ink);text-decoration:underline;text-underline-offset:5px;text-decoration-color:var(--line)}
.paper-link:hover{text-decoration-color:currentColor}
.paper-section :focus-visible{outline-color:var(--ink)}
.numbers{padding:100px var(--pad) 92px}
.numbers-head,.numbers-grid,.legend>*{max-width:1300px;margin-left:auto;margin-right:auto}
.numbers-head{display:grid;grid-template-columns:minmax(0,1.2fr) minmax(0,1fr);gap:8px 48px;align-items:end;margin-bottom:44px}
.numbers-head .eyebrow,.numbers-head h2{grid-column:1}
.numbers-head>p:not(.eyebrow){grid-column:2;grid-row:2;font:16px/1.7 var(--sans);color:var(--ink-muted);max-width:40ch}
.numbers-head .paper-link{grid-column:2}
.numbers-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));border-top:1px solid var(--ink)}
.number{padding:26px 22px 30px 0;border-bottom:1px solid var(--line)}
.number:not(:nth-child(4n+1)){padding-left:22px;border-left:1px solid var(--line)}
.number .figure{font:400 clamp(44px,4.6vw,68px)/1 var(--font-mono);letter-spacing:-.05em;white-space:nowrap;font-variant-numeric:tabular-nums}
.number .unit{margin-left:.18em;font-size:.42em;letter-spacing:0;color:var(--ink-muted)}
.number-label{margin-top:16px;font:14.5px/1.6 var(--sans);color:var(--ink)}
.number-date{margin-top:10px;font:11.5px/1.6 var(--font-mono);letter-spacing:.03em;color:var(--ink-soft)}
.legend{padding:96px var(--pad)}
.legend-head{margin-bottom:36px}
.legend-list{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:0;border-top:1px solid var(--ink)}
.legend-list>div{padding:24px 24px 26px 0;border-bottom:1px solid var(--line)}
.legend-list>div+div{padding-left:24px;border-left:1px solid var(--line)}
.legend-list dt .status{font-size:12px;color:var(--ink)}
.legend-list dd{margin-top:14px;font:16px/1.65 var(--sans);color:var(--ink-muted)}
.measured{margin-top:44px}
.measured p{max-width:72ch}
.measured h3{font-size:34px}
.measured p{margin-top:14px;font:16px/1.75 var(--sans);color:var(--ink-muted)}

/* The chapter rail: fixed beside wide pages, an inline list of the seven systems elsewhere. */
.chapter-rail{display:flex;flex-wrap:wrap;gap:0 12px;max-width:1480px;margin:0 auto;padding:30px var(--pad) 0}
.rail-title{width:100%;margin-bottom:6px;font:500 11.5px/1.6 var(--font-mono);letter-spacing:.16em;text-transform:uppercase;color:var(--ink-soft)}
.rail-link{display:inline-flex;align-items:center;gap:10px;min-height:44px;padding:8px 14px 8px 0;font:12px/1.3 var(--font-mono);letter-spacing:.08em;text-transform:uppercase;color:var(--ink-muted)}
.rail-number{color:var(--ink-soft)}
.rail-link:hover,.rail-link[aria-current]{color:var(--ink)}
.rail-link[aria-current] .rail-number{color:var(--amber)}
@media (min-width:1280px){
  .js .chapter-rail{position:fixed;z-index:20;left:14px;top:50%;transform:translateY(-50%);flex-direction:column;flex-wrap:nowrap;gap:0;margin:0;padding:0;opacity:0;pointer-events:none;transition:opacity .3s}
  .js.rail-visible .chapter-rail,.js .chapter-rail:focus-within{opacity:1;pointer-events:auto}
  .js .rail-title{display:none}
  .js .rail-link{position:relative;min-height:44px;width:44px;padding:8px 0 8px 14px}
  .js .rail-link::before{content:'';position:absolute;left:0;top:50%;width:8px;height:1px;background:currentColor;opacity:.5}
  .js .rail-link[aria-current]::before{width:10px;height:2px;margin-top:-.5px;background:var(--amber);opacity:1}
  .js .rail-name{display:none;position:absolute;left:46px;top:50%;transform:translateY(-50%);padding:6px 10px;background:#141414;border:1px solid rgba(255,255,255,.14);border-radius:8px;white-space:nowrap;pointer-events:none}
  .js .rail-link:hover .rail-name,.js .rail-link:focus-visible .rail-name{display:block}
}

/* Closing, reading path and footer. */
.closing-section{max-width:1480px;margin:0 auto;padding:110px var(--pad) 90px;text-align:center}
.closing-section h2{margin-top:22px;font-size:clamp(50px,6.6vw,104px);letter-spacing:-.04em}
.closing-section h2 span{display:block}
.closing-section h2 em{color:#d6d4ce}
.closing-section>p:not(.eyebrow){max-width:62ch;margin:26px auto 0;font:17px/1.75 var(--sans);color:var(--ink-muted)}
.closing-links{display:flex;flex-wrap:wrap;justify-content:center;align-items:center;gap:12px 28px;margin-top:32px}
.chapter-exit{max-width:1480px;margin:0 auto;padding:34px var(--pad) 30px;border-top:1px solid var(--line)}
.exit-kicker,.exit-small{font:11.5px/1.6 var(--font-mono);letter-spacing:.14em;text-transform:uppercase;color:var(--ink-soft)}
.exit-main{display:flex;flex-wrap:wrap;justify-content:space-between;align-items:end;gap:16px 30px;margin-top:22px}
.exit-title{margin-top:8px;font:36px/1.1 var(--font-serif);letter-spacing:-.03em}
.exit-next{display:inline-flex;align-items:center;gap:14px;min-height:48px;padding:12px 18px;border:1px solid var(--line);font:13px/1.3 var(--sans)}
.exit-next:hover{border-color:var(--ink)}
.exit-links{display:flex;flex-wrap:wrap;gap:4px 26px;margin-top:20px}
.exit-links a{display:inline-flex;align-items:center;min-height:44px;font:13px/1.3 var(--sans);color:var(--ink-muted)}
.exit-links a:hover{color:var(--ink)}
.site-footer{display:flex;flex-wrap:wrap;justify-content:space-between;align-items:center;gap:18px 40px;max-width:1480px;margin:0 auto;padding:30px var(--pad) calc(36px + env(safe-area-inset-bottom,0px));border-top:1px solid var(--line)}
.site-footer .brand{margin-right:0}
.site-footer .brand>span{font-size:24px}
.site-footer p{flex:1 1 320px;font:12px/1.8 var(--font-mono);color:var(--ink-soft)}
.site-footer nav{display:flex;flex-wrap:wrap;gap:0 22px}
.site-footer nav a{display:inline-flex;align-items:center;justify-content:center;min-height:44px;min-width:44px;font:13px/1.3 var(--sans);color:var(--ink-muted)}
.site-footer nav a:hover{color:var(--ink)}

@media (max-width:1100px){
  .site-nav a{padding-inline:10px;font-size:12.5px}
  .brand-sub{display:none}
  .numbers-grid{grid-template-columns:repeat(2,minmax(0,1fr))}
  .number:not(:nth-child(4n+1)){padding-left:0;border-left:0}
  .number:nth-child(even){padding-left:22px;border-left:1px solid var(--line)}
}
@media (max-width:900px){
  :root{--header:86px}
  .chapter,.hero{display:flex;flex-direction:column;align-items:stretch;gap:0;min-height:0;padding-top:84px;padding-bottom:78px}
  .hero{padding-top:calc(var(--header) + 44px)}
  .chapter-copy{display:contents}
  .chapter .eyebrow{order:0}
  .chapter h1,.chapter h2{order:1}
  .chapter-visual,.chapter.reverse .chapter-visual{order:2;position:relative;top:auto;margin-top:30px}
  .chapter-body{order:3}
  .chapter-equation{order:4}
  .hero-actions{order:5}
  .edition-pill{order:6}
  .feature-list{order:5}
  .feature-more{order:6}
  .chapter-bridge{order:7}
  .chapter h1{font-size:clamp(46px,11.5vw,72px)}
  .chapter h2{font-size:clamp(38px,9.6vw,60px)}
  .explanation-canvas{aspect-ratio:1.25;max-height:none}
  .numbers-head{display:block}
  .numbers-head>p:not(.eyebrow){margin-top:18px}
  .legend-list{grid-template-columns:1fr}
  .legend-list>div+div{padding-left:0;border-left:0}
}
@media (max-width:760px){
  .site-header{top:10px;height:60px;padding:7px 8px 7px 14px}
  .site-nav{display:none}
  .site-menu{display:block;margin-left:8px}
  .motion-toggle{padding:10px 13px}
  .motion-text{display:none}
  .brand>span{font-size:24px}
  .brand img{width:27px;height:27px}
  .chapter-body{font-size:16.5px}
  .visual-label{font-size:25px}
  .feature-list h3{font-size:23px}
  .feature-head{flex-direction:column-reverse;align-items:flex-start;gap:6px}
  .numbers,.legend{padding-top:72px;padding-bottom:70px}
  .number,.number:nth-child(even){padding:22px 14px 24px 0}
  .number:nth-child(even){padding-left:14px}
  .number .figure{font-size:clamp(34px,10.5vw,48px)}
  .number-label{font-size:14px}
  .closing-section{padding-top:80px;padding-bottom:64px}
  .closing-section h2 span{display:inline}
  .closing-links{flex-direction:column}
}
@media (max-width:370px){
  .brand>span{font-size:22px}
  .hero-actions{gap:6px 18px}
  .solid-link{padding-inline:16px}
  .feature-list h3{font-size:21.5px}
  .number .figure{font-size:30px}
}
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{transition:none!important;animation:none!important}
}
.noscript-note{max-width:1480px;margin:0 auto;padding:18px var(--pad);font:13px/1.7 var(--font-mono);color:var(--ink-muted)}