:root{color-scheme:dark;--ink:#f0eee8;--muted:#a6adb2;--line:#30383d;--accent:#b8d5e3;--bg:#000;--section:32px;--body:18px}
*{box-sizing:border-box}
html{background:var(--bg);color:var(--ink);font-family:ui-sans-serif,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif}
body{margin:0}p,h1,h2,h3,figure{margin:0}sup,sub{line-height:0}
a{color:inherit;text-decoration:none}a:hover{color:var(--accent)}
a:focus-visible,summary:focus-visible{outline:2px solid var(--accent);outline-offset:6px}
.masthead,main,footer{width:min(100%,1376px);margin-inline:auto;padding-inline:64px}
.masthead{height:112px;display:flex;justify-content:space-between;align-items:center;position:relative;z-index:5}
.brand{font:30px/1 Georgia,serif;letter-spacing:-.035em}.brand span{display:block;margin-top:9px;font:italic 11px/1.4 Georgia,serif;letter-spacing:.05em;color:var(--muted)}
.header-actions{display:flex;align-items:center;gap:40px;font-size:13px}.explore{display:flex;align-items:center;gap:10px}
.free{display:inline-block;border:1px solid #000;border-radius:4px;padding:3px 5px;background:#e0e9ed;color:#101010;letter-spacing:.07em;font:600 9px/1.2 ui-sans-serif,sans-serif;vertical-align:middle}
.menu summary{list-style:none;cursor:pointer;display:flex;align-items:center;gap:22px;padding:16px 0}.menu summary::-webkit-details-marker{display:none}.menu summary>span{font-size:22px;font-weight:300}.menu[open] summary>span{transform:rotate(45deg)}
.menu nav{position:absolute;right:64px;top:94px;width:370px;background:#0c0e10;border:1px solid var(--line);border-radius:12px;padding:14px 22px;box-shadow:0 18px 50px #000}
.menu nav a{display:flex;gap:17px;padding:15px 0;font-size:14px;border-bottom:1px solid var(--line)}.menu nav a:last-child{border:0}.menu nav a span{font-size:10px;color:var(--muted);padding-top:3px}.menu nav a[aria-current]{color:var(--accent)}
.chapters{width:min(calc(100% - 128px),1248px);margin:auto;display:flex;justify-content:space-between;gap:24px;border-block:1px solid var(--line)}
.chapters a{position:relative;display:flex;align-items:center;padding:20px 0;font-size:12px;line-height:1.5;color:var(--muted)}.chapters a:hover,.chapters a[aria-current]{color:var(--ink)}.chapters a[aria-current]:after{content:'';position:absolute;inset:auto 0 -1px;height:2px;background:var(--accent)}
/* One opening composition and one typographic hierarchy across the chapters. */
.hero{display:grid;grid-template-columns:minmax(0,1.12fr) minmax(0,1fr);gap:56px;align-items:center;padding:64px 0;border-bottom:1px solid var(--line)}
.hero-copy,.hero-art,.chapter-art{min-width:0}.chapter-meta{display:flex;gap:28px;margin-bottom:28px;color:var(--muted);font-size:10px;letter-spacing:.12em;text-transform:uppercase}
h1{font:400 clamp(44px,4.8vw,66px)/1.12 Georgia,serif;letter-spacing:-.045em}h1 em,h2 em{color:#c0d3dc;font-weight:400}
.lead{font:21px/1.65 Georgia,serif;color:#d0d0cc;margin-top:26px}.byline{font-size:11px;line-height:1.7;color:var(--muted);margin-top:26px;letter-spacing:.02em}.byline span{margin-inline:7px}
.hero img{display:block;width:100%;height:auto;max-height:550px;object-fit:contain;border-radius:12px}.hero figcaption{text-align:center}
.hero.full-art:not(.julia-hero){display:block}.hero.full-art:not(.julia-hero) .hero-copy{max-width:900px}.hero.full-art:not(.julia-hero) .chapter-art{margin-top:32px}
[data-factoring-figure]{display:block;width:100%;height:500px}
/* Prose always reads down a single column. Selected images occupy the adjacent space. */
article{padding-top:8px}h2{font:400 var(--section)/1.3 Georgia,serif;letter-spacing:-.025em;margin-bottom:20px}
h3{font:400 23px/1.35 Georgia,serif}p{font-size:var(--body);line-height:1.85;color:#bfc3c6}
.passage{width:100%;max-width:740px;margin:52px 0}.passage p+p,.image-passage p+p{margin-top:20px}
.illustrated-passage,.image-passage{display:grid;grid-template-columns:minmax(0,1.12fr) minmax(0,1fr);gap:56px;align-items:center;margin:64px 0}
.illustrated-passage .passage{margin:0;max-width:none}.illustrated-passage figure,.image-passage figure{min-width:0;margin:0}.image-passage .world-image{order:2}
.world-plate img,.world-image img{display:block;width:100%;height:auto;max-height:540px;object-fit:contain;border-radius:12px}.world-plate{margin:52px 0}
figcaption{font-size:11px;line-height:1.65;color:var(--muted);margin-top:14px}
.statement{max-width:740px;margin:48px 0;padding-left:24px;border-left:2px solid #5a7180}.statement p{font:italic 24px/1.6 Georgia,serif;color:#d8e1e5}
.editor-note{font-size:12px;line-height:1.8;color:var(--muted);border-left:1px solid #596874;padding-left:18px;max-width:740px;margin:32px 0}
.eyebrow,.section-label{font-size:10px;text-transform:uppercase;letter-spacing:.15em;color:#a8bac5;line-height:1.6}
/* Diagrams retain their own labels, within a consistent figure boundary. */
.diagram{margin:52px 0;padding:28px 0;border-block:1px solid var(--line)}.diagram>.eyebrow{margin-bottom:28px}
.faculties,.sequence{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:40px}.faculties span,.sequence span{font-size:11px;color:var(--muted)}.faculties h3,.sequence h3{margin:14px 0}.faculties p,.sequence p{font-size:16px;line-height:1.75}
.sequence{list-style:none;margin:0;padding:0}.sequence li{position:relative}.sequence li:not(:last-child):after{content:'→';position:absolute;right:-27px;top:48px;color:#86a9bc}
.doubling{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:22px}.points{display:grid;grid-template-columns:repeat(4,10px);gap:6px;align-content:center;min-height:145px}.points i{width:10px;height:10px;border-radius:50%;background:#bcddeb}.equation{font:26px/1.6 Georgia,serif;color:#e1edf3;white-space:nowrap}
.equation-visual>.eyebrow{display:none}.equation-pair{display:grid;grid-template-columns:1fr 1fr;gap:36px}.equation-pair span{font-size:13px;color:var(--muted)}.equation-pair .equation{font-size:32px;margin-top:12px}
.wide-diagram svg,.profile-art svg{display:block;width:100%;height:auto;max-height:440px}.diagram svg line,.profile-art svg line{stroke:#628a9f;stroke-width:1.4}.diagram svg circle,.profile-art svg circle{fill:#c1dfed;stroke:#000;stroke-width:3}
.diagram svg text,.profile-art svg text{fill:#d4e4ed;font:23px Georgia,serif;text-anchor:middle}.diagram svg text.sub{fill:#95a7b2;font:14px ui-sans-serif,sans-serif}.diagram svg .focus-region,.profile-art svg .focus-region{fill:#0c1921;stroke:#66828f;stroke-width:1}.diagram svg text.region-label,.profile-art svg text.region-label{font:12px ui-sans-serif,sans-serif;letter-spacing:4px;fill:#a6c1d0}
.compact-diagram,.profile-compact{display:none}
.concept-tiles{border-top:1px solid var(--line)}.concept-tiles details{border-bottom:1px solid var(--line)}.concept-tiles summary{list-style:none;cursor:pointer;display:flex;align-items:center;justify-content:space-between;gap:24px;padding:22px 0}.concept-tiles summary::-webkit-details-marker{display:none}.concept-tiles h3{font-size:23px}.concept-tiles .expand b{font-size:24px;font-weight:300}.concept-tiles details[open] .expand b{display:inline-block;transform:rotate(45deg)}.concept-tiles details p{max-width:740px;padding-bottom:24px}.symbol{font:28px Georgia,serif}.expand{display:flex;gap:12px;align-items:center;font-size:12px;color:var(--muted)}
.conversation{max-width:740px}.conversation p{font:22px/1.6 Georgia,serif;padding:20px 0;border-bottom:1px solid var(--line)}
/* Directory, reach and contact use the same section title size. */
.contents-index{margin:64px 0}.contents-index>.section-label{margin-bottom:24px}.contents-index>a{display:grid;grid-template-columns:150px 32px 1fr 26px;gap:24px;align-items:center;padding:22px 0;border-top:1px solid var(--line)}.chapter-thumb{width:150px;height:110px;object-fit:contain;border-radius:8px}.chapter-number{font-size:11px;color:var(--muted)}.contents-index h3{font-size:26px}.index-arrow{font-size:24px;color:var(--accent)}
.reach{margin:48px 0 64px}.reach-heading{display:flex;align-items:start;justify-content:space-between;gap:28px;margin-bottom:24px}.reach-heading h2{margin:0}.reach-heading p{font-size:12px}.reach-heading strong{font-size:18px;font-weight:400;color:var(--ink)}.reach-globe{display:block;border:0;width:100%;height:850px;background:#000;border-radius:12px}.reach-note{font-size:11px;line-height:1.7;color:var(--muted);margin-top:16px}.reach-note a{color:var(--accent);margin-left:12px}
.invitation{max-width:900px;margin:64px 0;padding-top:32px;border-top:1px solid var(--line)}.invitation h2{margin-top:20px}.invitation p{max-width:740px}.button{display:inline-flex;align-items:center;gap:36px;margin-top:26px;border:1px solid #90a8b6;border-radius:8px;padding:17px 22px;background:#e0e9ed;color:#0b1115;font-size:14px}.button:hover{color:#0b1115;background:#fff}.text-link{display:block;width:fit-content;font-size:13px;color:var(--accent);margin-top:20px}
.next{display:flex;align-items:center;justify-content:space-between;gap:28px;padding-top:24px;margin:64px 0 48px;border-top:1px solid var(--line)}.next>a{display:flex;justify-content:space-between;align-items:center;gap:24px;font:22px/1.4 Georgia,serif}.next>a span{font:23px/1 ui-sans-serif,sans-serif;color:var(--accent)}
footer{border-top:1px solid var(--line);padding-top:36px;padding-bottom:44px;display:flex;justify-content:space-between;align-items:start;gap:30px}footer>p{font-size:12px;color:var(--muted)}footer>div{display:grid;gap:20px;font-size:12px;color:var(--muted)}
.skip{position:fixed;top:-80px;left:20px;padding:15px;background:#fff;color:#000;z-index:20}.skip:focus{top:15px}
@media(max-width:1100px){
.masthead,main,footer{padding-inline:42px}.menu nav{right:42px}.chapters{width:calc(100% - 84px);gap:18px}.chapters a{font-size:11px}
.hero,.illustrated-passage,.image-passage{gap:36px}h1{font-size:49px}.lead{font-size:20px}
}
@media(max-width:740px){
:root{--section:28px;--body:17px}.masthead,main,footer{padding-inline:24px}.masthead{height:96px}.brand{font-size:27px}.brand span{font-size:10px}.header-actions{gap:22px;font-size:12px}.explore>span:last-child{display:none}.menu summary{gap:11px}.menu nav{right:24px;top:82px;width:min(370px,calc(100vw - 48px))}
.chapters{width:calc(100% - 48px);display:grid;grid-template-columns:1fr 1fr;gap:0 20px;padding:8px 0}.chapters a{font-size:11px;padding:10px 0}.chapters a[aria-current]:after{display:none}.chapters a[aria-current]{color:var(--accent)}
.hero{grid-template-columns:1fr;gap:28px;padding:40px 0}.chapter-meta{font-size:9px;gap:22px;margin-bottom:24px}h1{font-size:42px}.lead{font-size:20px;margin-top:24px}.byline{font-size:10px;margin-top:24px}.hero-art,.chapter-art{width:100%;max-width:480px;margin:auto}.hero img{max-height:420px}
.passage{margin:40px 0}.illustrated-passage,.image-passage{grid-template-columns:1fr;gap:28px;margin:48px 0}.illustrated-passage .world-plate{max-width:480px;width:100%;margin:auto}.image-passage .world-image{order:0}.statement{margin:40px 0;padding-left:18px}.statement p{font-size:21px}.diagram{margin:40px 0;padding:24px 0}
.faculties,.sequence{grid-template-columns:1fr;gap:32px}.faculties>div+div{border-top:1px solid var(--line);padding-top:24px}.faculties h3,.sequence h3{font-size:23px}.sequence{gap:42px}.sequence li:not(:last-child):after{content:'↓';top:auto;right:auto;left:0;bottom:-30px}
.doubling{grid-template-columns:repeat(3,minmax(0,1fr));gap:24px 12px}.points{grid-template-columns:repeat(4,9px);gap:5px;min-height:130px}.points i{width:9px;height:9px}.equation{font-size:22px}.equation-pair{gap:18px}.equation-pair .equation{font-size:27px}
.wide-diagram,.profile-art svg{display:none}.compact-diagram,.profile-compact{display:block}.compact-diagram .origin,.profile-compact .origin{font:22px/1.5 Georgia,serif;color:#c6deeb;padding:14px 0}.compact-diagram ul{list-style:none;margin:18px 0 18px 8px;padding-left:24px;border-left:1px solid #658191}.compact-diagram li{position:relative;padding:16px 0;font:22px/1.4 Georgia,serif}.compact-diagram li:before{content:'';position:absolute;left:-28px;top:27px;width:7px;height:7px;border-radius:50%;background:#c0dfef}.compact-diagram li span{display:block;font:14px/1.7 ui-sans-serif,sans-serif;color:var(--muted);margin-top:6px}.course-focus{padding:22px 18px;border:1px solid #667e8c;border-radius:12px;background:#0c1921;margin:18px 0}.course-focus h3{margin-bottom:12px}.course-focus p{font-size:16px}.profile-compact{text-align:center}
.concept-tiles h3{font-size:22px}.conversation p{font-size:20px}.contents-index>a{grid-template-columns:86px 1fr 20px;gap:16px}.chapter-thumb{width:86px;height:82px}.chapter-number{display:none}.contents-index h3{font-size:22px}
.reach-heading{display:block}.reach-heading h2{margin-bottom:16px}.reach-globe{height:800px}.reach-note a{display:block;margin:10px 0 0}.next{flex-direction:column;align-items:start;gap:16px;margin:48px 0}.next>a{width:100%;font-size:22px}.button{gap:24px;font-size:13px}
footer{flex-wrap:wrap}footer>div{width:100%;display:flex;justify-content:space-between;flex-wrap:wrap;gap:20px}
}
@media(max-width:380px){.masthead,main,footer{padding-inline:20px}.chapters{width:calc(100% - 40px)}.header-actions{gap:16px}.brand{font-size:24px}.brand span{font-size:9px}.menu nav{right:20px;width:calc(100vw - 40px)}}