:root{--paper:#f8f8f0;--ink:#202d29;--muted:#6f7971;--teal:#176852;--line:#dce1d5;--white:#fffef8;--serif:Georgia,'Times New Roman',serif}*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--paper);color:var(--ink);font:16px/1.7 'Segoe UI',Arial,sans-serif}a{color:inherit;text-decoration:none}button,input{font:inherit}button,a,input{ -webkit-tap-highlight-color:transparent}a,button{transition:background .2s,transform .2s,color .2s}a:focus-visible,button:focus-visible,input:focus-visible{outline:3px solid #cb762c;outline-offset:5px}header{max-width:1400px;margin:auto;padding:25px 4.5%;display:flex;align-items:center;justify-content:space-between;gap:24px;border-bottom:1px solid var(--line)}.brand{display:flex;align-items:center;font-size:23px;font-weight:750;letter-spacing:-1px;white-space:nowrap}.brand>span:not(.brand-icon){font-weight:400}.brand-icon{display:grid;place-items:center;width:34px;height:38px;background:var(--teal);color:white;margin-right:10px;border-radius:7px;font:28px var(--serif)}.brand i{font-style:normal;color:#b5beb0;margin:0 17px;font-weight:300}.brand small{font-size:8px;letter-spacing:1px;color:var(--muted)}nav{display:flex;gap:25px;align-items:center;font-size:13px;font-weight:600}nav a:hover,.text-link:hover{color:var(--teal)}nav a[aria-current]{color:var(--teal);text-decoration:underline;text-underline-offset:6px}.nav-cta{border:1px solid var(--teal);padding:9px 16px;border-radius:6px;color:var(--teal)}.menu-toggle{display:none}.skip{position:absolute;top:-100px}.skip:focus{top:0;background:white;z-index:10;padding:10px}main{max-width:1240px;margin:auto;padding:0 30px}.hero{display:grid;grid-template-columns:1.1fr 1fr;gap:30px;align-items:center;min-height:620px;padding:64px 0 45px}.eyebrow{font-size:10px;font-weight:700;letter-spacing:1.7px;color:var(--teal);margin-bottom:23px}.dot{display:inline-block;width:6px;height:6px;background:var(--teal);border-radius:50%;margin-right:8px}h1,h2,h3,p{margin-top:0}h1{font:clamp(38px,5.5vw,76px)/1.04 var(--serif);letter-spacing:-3px;font-weight:400;margin-bottom:26px}h1 em{font-weight:400;color:var(--teal)}.teal{color:var(--teal)}.hero-copy>p{color:var(--muted);max-width:400px;font-size:15px;line-height:1.9}.actions{display:flex;align-items:center;gap:25px;margin:30px 0 38px}.button{display:inline-flex;align-items:center;justify-content:space-between;gap:30px;padding:13px 21px;background:var(--teal);color:white;border-radius:6px;font-size:13px;font-weight:600}.button:hover{background:#104d3d;transform:translateY(-2px)}.text-link{font-size:13px;font-weight:600}.hero-foot{display:flex;gap:23px;font-size:9px;letter-spacing:1px;color:var(--muted)}.math-art{position:relative;min-width:0;background-image:radial-gradient(#b8c6af 0.65px,transparent .65px);background-size:19px 19px;border-radius:50%;padding:30px 0}.math-art svg{width:100%;height:auto;display:block}.art-label,.art-index{font-size:8px;letter-spacing:1.5px;color:var(--muted);display:block;text-align:center}.equation-tag{position:absolute;right:4%;bottom:70px;background:var(--white);box-shadow:0 8px 30px #254b2910;border:1px solid var(--line);border-radius:9px;padding:12px 22px;transform:rotate(-5deg)}.equation-tag small{font-size:7px;letter-spacing:1.5px;display:block;color:var(--muted)}.equation-tag span{font:26px var(--serif)}.section-heading{display:flex;justify-content:space-between;align-items:end;gap:20px;margin:26px 0}.section-heading .eyebrow{margin-bottom:10px}h2{font:32px/1.25 var(--serif);letter-spacing:-.8px;margin-bottom:0}.feature-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:18px}.feature{position:relative;border:1px solid var(--line);border-radius:10px;padding:26px;background:#fcfcf6}.feature:nth-child(2){background:#edf1e6}.feature:nth-child(3){background:#f3eee4}.feature:hover{transform:translateY(-5px);border-color:var(--teal)}.tile-icon{font:29px var(--serif);display:block;color:var(--teal);margin-bottom:24px}.tile-number{font-size:9px;letter-spacing:1px;color:var(--muted)}.feature h3{font:23px var(--serif);margin:10px 0}.feature p{font-size:13px;max-width:260px;color:var(--muted);margin-bottom:22px}.card-arrow{position:absolute;bottom:18px;right:23px;font-size:24px}.geometry{margin:65px 0}.model-grid{display:grid;grid-template-columns:1fr 1fr;gap:20px}.model-grid article{border:1px solid var(--line);border-radius:12px;overflow:hidden;background:var(--white)}.model-stage{background:radial-gradient(ellipse,#dfebdf,transparent)}model-viewer{display:block}model-viewer:not(:defined){display:grid;place-items:center}model-viewer span{font-size:12px;color:var(--teal)}.model-caption{padding:20px 25px;display:flex;gap:25px;border-top:1px solid var(--line)}.model-caption h3{font:24px var(--serif)}.model-caption p{font-size:12px;color:var(--muted);margin:0}.muted{color:var(--muted);font-size:12px}.closing{text-align:center;border-top:1px solid var(--line);padding:45px 10px}.closing>span{font-size:9px;letter-spacing:2px;color:var(--teal)}.closing h2{margin:16px 0 25px}.source-note{font-size:10px;color:var(--muted);text-align:center;max-width:800px;margin:0 auto 30px}footer{border-top:1px solid var(--line);max-width:1400px;padding:27px 4.5%;margin:auto;display:flex;justify-content:space-between;align-items:center;gap:20px;font-size:10px;color:var(--muted)}footer .brand{font-size:17px;color:var(--ink)}.article main{max-width:920px;padding-top:55px;padding-bottom:70px}.article h1{font-size:45px;line-height:1.15;letter-spacing:-1.5px}.article h2{margin-top:40px;margin-bottom:25px}.article h3{font-size:18px;margin-top:26px;margin-bottom:12px;color:var(--teal)}.article p{line-height:1.95}.article main>p{background:var(--white);padding:20px 25px;border:1px solid var(--line);border-radius:8px}.article main>br,.directory main>br,.quiz br,.result main>br{display:none}hr{border:0;border-top:1px solid var(--line);margin:30px 0}.article strong{font-weight:650}.article table{border-collapse:collapse;display:block;overflow-x:auto;width:100%;background:var(--white);border:1px solid var(--line)}td,th{padding:14px 20px;border:1px solid var(--line);text-align:center}th{background:#e8eee3}.note{padding:15px 20px;background:#edf1e6;border-left:3px solid var(--teal);border-radius:5px;font-size:13px;color:#4d6156}.directory main{padding-top:55px;padding-bottom:65px;min-height:70vh}.directory h1{font-size:49px;max-width:820px}.directory main>a{display:block;padding:24px 30px;margin:15px 0;background:var(--white);border:1px solid var(--line);border-radius:10px;font-size:20px;color:var(--teal)}.directory main>a:hover{transform:translateX(5px);border-color:var(--teal)}.directory main>a:after{content:'↗';float:right}.directory main>a button{background:none;border:0;color:inherit;padding:0}.directory main>div:not(.eyebrow){display:grid;grid-template-columns:repeat(3,1fr);gap:22px}.directory main>div>a{background:var(--white);border:1px solid var(--line);border-radius:12px;overflow:hidden;display:flex;flex-direction:column}.directory img{width:100%;height:280px;object-fit:cover;object-position:top;filter:grayscale(1)}.directory main>div>a span{padding:20px;font:20px var(--serif)}.quiz main{max-width:850px;padding-top:45px;padding-bottom:70px;min-height:78vh}.quiz-meta{display:flex;justify-content:space-between;align-items:center;font-size:12px}.quiz-meta>span:first-child{font-size:20px;font-weight:600}progress{width:100%;height:5px;display:block;margin:20px 0 28px;accent-color:var(--teal)}.question-card{background:var(--white);border:1px solid var(--line);padding:35px;border-radius:16px}.question-card h2{font:25px/1.55 var(--serif);margin-bottom:30px;letter-spacing:0}.question-card>button{display:block;position:relative;width:100%;text-align:left;background:var(--paper);border:1px solid var(--line);padding:15px 20px;border-radius:8px;margin:12px 0;cursor:pointer;line-height:1.6}.question-card>button:hover:not(:disabled){border-color:var(--teal);background:#edf2e6}.question-card>button.correct{background:#deefdf;border-color:#398052}.question-card>button.wrong{background:#f7e4de;border-color:#ac5643}.question-card>button:disabled{color:var(--ink);cursor:default}.option-letter{display:inline-grid;place-items:center;width:28px;height:28px;border:1px solid var(--line);border-radius:5px;margin-right:15px;font-size:12px;color:var(--teal)}.question-card hr{display:none}.question-card>a{font-size:12px}.question-card>a button{border:0;background:none;color:var(--teal);cursor:pointer}.feedback{margin-top:24px;padding:17px;background:#edf1e6;border-radius:8px}.feedback a{display:inline-block;margin-top:10px;color:var(--teal);font-weight:650}.result main{text-align:center;min-height:70vh;padding:80px 20px}.result h1{font-size:50px}.result h2{margin:20px}.result button{background:var(--teal);border:0;border-radius:6px;padding:12px 20px;color:white;font-size:14px;margin:15px;cursor:pointer}.toc{margin:20px 0 35px;padding:20px;background:#edf1e6;border-radius:8px}.toc summary{cursor:pointer;color:var(--teal);font-weight:600}.toc a{display:block;padding:5px 0;font-size:13px}h2,h3{scroll-margin-top:25px}@media(min-width:1450px){.hero{min-height:680px}}@media(max-width:1050px){.brand small,.brand i{display:none}nav{gap:15px}.hero{min-height:560px}h1{font-size:60px}.hero-foot{gap:12px}}@media(max-width:760px){header{padding:18px 22px;flex-wrap:wrap}.menu-toggle{display:block;border:1px solid var(--line);background:transparent;border-radius:6px;padding:5px 12px;color:var(--teal)}nav{display:none;width:100%;flex-direction:column;align-items:stretch;padding:10px 0}nav.open{display:flex}nav a{padding:9px}.hero{grid-template-columns:1fr;padding:40px 0 30px;gap:30px}.hero h1{font-size:60px}.hero-copy>p{max-width:100%}.hero-foot{gap:20px}.math-art{max-width:480px;width:100%;margin:auto}.actions{gap:18px;flex-wrap:wrap}.feature-grid{grid-template-columns:1fr}.feature{padding:24px}.tile-icon{margin-bottom:15px}.feature p{max-width:85%}.section-heading{align-items:start;flex-direction:column}h2{font-size:29px}.model-grid{grid-template-columns:1fr}.model-caption{gap:20px}.geometry{margin:45px 0}main{padding:0 22px}footer{flex-direction:column;text-align:center;gap:12px}.directory h1,.article h1{font-size:35px}.directory main>div:not(.eyebrow){grid-template-columns:1fr}.directory img{height:330px}.question-card{padding:22px}.question-card h2{font-size:22px;overflow-wrap:anywhere}.quiz-meta{gap:10px;flex-wrap:wrap}.article main>p{padding:15px;overflow-wrap:anywhere}.directory main>a{font-size:17px;padding:20px}.result h1{font-size:38px}.brand{font-size:21px}.quiz main{padding-top:30px}.note{overflow-wrap:anywhere}}@media(prefers-reduced-motion:reduce){*{scroll-behavior:auto!important;transition:none!important}}@media print{header,footer,.toc,.menu-toggle{display:none}body{background:white;color:black}main{max-width:none!important}.article main>p{break-inside:avoid;border:0;padding:0}.article h2{break-after:avoid}}

/* Midnight edition — semantic surfaces shared across the full collection. */
:root{--accent-fill:#176852;--accent-ink:#fff;--surface-soft:#edf1e6;--surface-alt:#f3eee4;--shadow:0 18px 55px #1632290b;--glow:transparent}
:root[data-theme="dark"]{color-scheme:dark;--paper:#0b1219;--ink:#e7eee9;--muted:#a1b2b4;--teal:#7de3c0;--line:#293941;--white:#121e27;--accent-fill:#85e5c3;--accent-ink:#0b2822;--surface-soft:#152a2c;--surface-alt:#202732;--shadow:0 18px 55px #0003;--glow:#4bcba70b}
:root[data-theme="light"]{color-scheme:light}
body{background:radial-gradient(ellipse at 80% 10%,var(--glow),transparent 40%),var(--paper)}header{position:relative;gap:18px}.brand small{display:none}.brand i{display:none}nav{gap:18px;font-size:12px}.header-controls{display:flex;gap:9px;align-items:center;order:3}.theme-toggle{display:inline-flex;align-items:center;justify-content:center;gap:8px;background:var(--white);color:var(--ink);border:1px solid var(--line);border-radius:30px;min-height:38px;padding:6px 13px;cursor:pointer;font-size:11px;white-space:nowrap}.theme-toggle:hover{border-color:var(--teal);background:var(--surface-soft)}.theme-icon{font-size:20px;line-height:1}.ask-ai{display:inline-flex;align-items:center;justify-content:center;gap:10px;background:var(--surface-soft);color:var(--teal);border:1px solid var(--line);padding:9px 15px;border-radius:7px;white-space:nowrap;font-size:13px;font-weight:650}.ask-ai:hover{border-color:var(--teal);transform:translateY(-2px)}.button,.result button,.brand-icon{background:var(--accent-fill);color:var(--accent-ink)}.button:hover{background:var(--accent-fill);filter:brightness(1.08)}.feature{background:var(--white);box-shadow:var(--shadow);overflow:hidden}.feature:nth-child(2){background:var(--surface-soft)}.feature:nth-child(3){background:var(--surface-alt)}.feature:before{content:'';position:absolute;inset:0 0 auto;height:2px;background:linear-gradient(90deg,transparent,var(--teal),transparent);opacity:0;transition:opacity .25s}.feature:hover:before{opacity:1}.feature:hover{box-shadow:0 20px 45px #0002}.tile-icon{width:53px;height:53px;display:grid;place-items:center;border:1px solid var(--line);border-radius:13px;background:var(--paper)}.equation-tag{box-shadow:var(--shadow)}.hero-foot{border-top:1px solid var(--line);padding-top:20px;width:fit-content}.ai-banner{display:flex;align-items:center;gap:25px;padding:32px 36px;margin:40px 0;background:linear-gradient(120deg,var(--surface-soft),var(--white));border:1px solid var(--line);border-radius:15px}.ai-banner .eyebrow{margin-bottom:8px}.ai-banner p{margin:8px 0 0;color:var(--muted);font-size:14px}.ai-banner>.ask-ai{margin-left:auto;background:var(--accent-fill);color:var(--accent-ink);padding:13px 24px}.ai-symbol{display:grid;place-items:center;font-size:38px;color:var(--teal);width:76px;height:76px;border-radius:22px;background:var(--paper);border:1px solid var(--line);flex-shrink:0}.note,.toc,.feedback{background:var(--surface-soft);color:var(--ink)}th{background:var(--surface-soft)}.model-stage{background:radial-gradient(ellipse,var(--surface-soft),transparent)}.question-card>button:hover:not(:disabled){background:var(--surface-soft)}.quiz progress{border:0;border-radius:9px;overflow:hidden;background:var(--line)}progress::-webkit-progress-bar{background:var(--line)}progress::-webkit-progress-value{background:var(--teal);border-radius:9px}progress::-moz-progress-bar{background:var(--teal)}.article main>p{box-shadow:var(--shadow)}.article .note{background:var(--surface-soft)}.directory main>div>a:hover{transform:translateY(-5px);border-color:var(--teal)}.directory img{transition:filter .3s}.directory a:hover img{filter:grayscale(0)}.skip:focus{background:var(--white);color:var(--ink)}
[data-theme="dark"] .math-art{background-image:radial-gradient(#4c6e705c .7px,transparent .7px)}[data-theme="dark"] .math-art svg g[stroke="#177464"]{stroke:#7de3c0}[data-theme="dark"] .math-art svg g[stroke="#c1c9bb"]{stroke:#5c7877}[data-theme="dark"] .math-art svg g[fill="#196151"]{fill:#92d9cd}[data-theme="dark"] .math-art svg stop:first-child{stop-color:#236f64}[data-theme="dark"] .math-art svg stop:last-child{stop-color:#0b1219}[data-theme="dark"] .math-art svg>circle:first-of-type{opacity:.5}[data-theme="dark"] .question-card>button.correct{background:#173c32;border-color:#72cfa8}[data-theme="dark"] .question-card>button.wrong{background:#442a30;border-color:#ef9a9d}[data-theme="dark"] .result main a{color:var(--teal)!important}[data-theme="dark"] .nav-cta:hover{background:var(--surface-soft)}[data-theme="dark"] .model-grid article{box-shadow:var(--shadow)}
@media(min-width:761px) and (max-width:1100px){header{flex-wrap:wrap}header nav{order:4;width:100%;justify-content:center;padding-top:10px}.header-controls{margin-left:auto}}
@media(max-width:760px){header{gap:10px}.header-controls{margin-left:auto;order:0}header nav{order:4}.theme-toggle{padding:6px 10px}.theme-label{display:none}.theme-icon{font-size:21px}.menu-toggle{min-height:38px}.brand{font-size:20px}.brand-icon{width:29px;height:33px;margin-right:7px}.ai-banner{flex-wrap:wrap;padding:25px;gap:18px}.ai-symbol{width:50px;height:50px;border-radius:14px;font-size:28px}.ai-banner>div:nth-child(2){flex:1;min-width:175px}.ai-banner h2{font-size:26px}.ai-banner>.ask-ai{margin-left:0;width:100%}.hero h1{font-size:clamp(43px,12vw,60px)}.hero-foot{gap:12px;font-size:8px}.directory main>a.ask-ai{display:flex;justify-content:space-between}.directory main>a.ask-ai:after{content:none}}
@media print{:root[data-theme]{--paper:white;--white:white;--ink:black;--muted:#444;--teal:#164d40;--surface-soft:#eee;--line:#aaa;color-scheme:light}body{background:white}.header-controls,.ai-banner{display:none}}