/* Fonts are served from this site (assets/fonts). No request is made to any third party. */
@font-face{font-family:'Nunito';font-style:normal;font-weight:200 1000;font-display:swap;src:url(../fonts/nunito-latin-wght-normal.woff2) format('woff2')}
@font-face{font-family:'Montserrat';font-style:normal;font-weight:100 900;font-display:swap;src:url(../fonts/montserrat-latin-wght-normal.woff2) format('woff2')}
@font-face{font-family:'JetBrains Mono';font-style:normal;font-weight:500;font-display:swap;src:url(../fonts/jetbrains-mono-latin-500-normal.woff2) format('woff2')}
@font-face{font-family:'JetBrains Mono';font-style:normal;font-weight:700;font-display:swap;src:url(../fonts/jetbrains-mono-latin-700-normal.woff2) format('woff2')}
/* Physimations shared styles. Compact headings, light and dark themes, one accent colour per major section. */
:root{
  --bg:#ffffff;--soft:#f3f8fe;--card:#ffffff;--ink:#0f2a4a;--ink-soft:#52677f;--line:#e1eaf5;
  --blue:#2878d0;--blue-t:#e8f2fd;
  --brand:var(--blue);--brand-t:var(--blue-t);
  --red:#e8341f;--red-t:#ffebe8;
  --yellow:#b88700;--yellow-t:#fff6d2;--yellow-disc:#ffd52a;
  --green:#2a9d5c;--green-t:#e4f6eb;
  --indigo:#5b5bd6;--indigo-t:#ecebfd;
  --navy:#0b2545;--navy-t:#e6ebf3;
  --cyan:#0a8fb0;--cyan-t:#e0f6fb;
  --f-display:'Nunito','Simply Rounded Bold','Arial Rounded MT Bold',system-ui,sans-serif;
  --f-body:'Montserrat',system-ui,-apple-system,'Segoe UI',sans-serif;
  --f-mono:'JetBrains Mono',ui-monospace,SFMono-Regular,Menlo,monospace;
  color-scheme:light;
}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]){
  --bg:#0c1a2e;--soft:#10233d;--card:#102640;--ink:#eaf1fb;--ink-soft:#a5b7d0;--line:#1f3555;
  --blue:#5aa0f0;--blue-t:rgba(90,160,240,.14);
  --brand:var(--blue);--brand-t:var(--blue-t);
  --red:#ff7a68;--red-t:rgba(255,122,104,.14);
  --yellow:#ffd52a;--yellow-t:rgba(255,213,42,.12);
  --green:#5fd493;--green-t:rgba(95,212,147,.13);
  --indigo:#9a9af2;--indigo-t:rgba(154,154,242,.15);
  --navy:#9fb8da;--navy-t:rgba(159,184,218,.13);
  --cyan:#4fd6f2;--cyan-t:rgba(79,214,242,.13);
  color-scheme:dark}}
:root[data-theme="dark"]{
  --bg:#0c1a2e;--soft:#10233d;--card:#102640;--ink:#eaf1fb;--ink-soft:#a5b7d0;--line:#1f3555;
  --blue:#5aa0f0;--blue-t:rgba(90,160,240,.14);
  --brand:var(--blue);--brand-t:var(--blue-t);
  --red:#ff7a68;--red-t:rgba(255,122,104,.14);
  --yellow:#ffd52a;--yellow-t:rgba(255,213,42,.12);
  --green:#5fd493;--green-t:rgba(95,212,147,.13);
  --indigo:#9a9af2;--indigo-t:rgba(154,154,242,.15);
  --navy:#9fb8da;--navy-t:rgba(159,184,218,.13);
  --cyan:#4fd6f2;--cyan-t:rgba(79,214,242,.13);
  color-scheme:dark}

*{box-sizing:border-box}
html{scroll-behavior:smooth;scroll-padding-top:96px}
body{margin:0;background:var(--bg);color:var(--ink);font-family:var(--f-body);font-size:16px;line-height:1.7;-webkit-font-smoothing:antialiased}
h1,h2,h3{font-family:var(--f-display);font-weight:800;line-height:1.15;margin:0;text-wrap:balance;letter-spacing:-.005em}
p{margin:0}a{color:inherit}
svg{display:block}
.wrap{max-width:1160px;margin:0 auto;padding-left:max(24px,env(safe-area-inset-left,0px));padding-right:max(24px,env(safe-area-inset-right,0px))}
:focus-visible{outline:3px solid var(--brand);outline-offset:3px;border-radius:8px}
.eyebrow{font-size:12px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--brand);margin-bottom:12px}

/* colour hooks */
[data-c="blue"]{--c:var(--blue);--ct:var(--blue-t);--cd:var(--blue);--cdi:#fff;--bn:#2f6bff;--bt:#fff;--bnn:rgba(255,255,255,.2)}
[data-c="red"]{--c:var(--red);--ct:var(--red-t);--cd:var(--red);--cdi:#fff;--bn:#e5372b;--bt:#fff;--bnn:rgba(255,255,255,.2)}
[data-c="yellow"]{--c:var(--yellow);--ct:var(--yellow-t);--cd:var(--yellow-disc);--cdi:#171717;--bn:#ffd23f;--bt:#1c1500;--bnn:rgba(0,0,0,.1)}
[data-c="green"]{--c:var(--green);--ct:var(--green-t);--cd:var(--green);--cdi:#fff;--bn:#5fd8a0;--bt:#06261a;--bnn:rgba(0,0,0,.1)}
[data-c="indigo"]{--c:var(--indigo);--ct:var(--indigo-t);--cd:var(--indigo);--cdi:#fff;--bn:#5b4bd9;--bt:#fff;--bnn:rgba(255,255,255,.2)}
[data-c="cyan"]{--c:var(--cyan);--ct:var(--cyan-t);--cd:#19b8d8;--cdi:#03222b;--bn:#3bd9f2;--bt:#04222b;--bnn:rgba(0,0,0,.1)}
[data-c="navy"]{--c:var(--navy);--ct:var(--navy-t);--cd:#0b2545;--cdi:#fff;--bn:#0b2545;--bt:#fff;--bnn:rgba(255,255,255,.18)}
:root[data-theme="dark"] [data-c="navy"]{--cd:#9fb8da;--cdi:#0b2545}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]) [data-c="navy"]{--cd:#9fb8da;--cdi:#0b2545}}
.disc{width:44px;height:44px;border-radius:50%;display:grid;place-items:center;background:var(--cd);color:var(--cdi);flex:none}
.disc svg{width:22px;height:22px}

/* header */
header.top{position:sticky;top:env(safe-area-inset-top,0px);z-index:40;background:var(--bg);border-bottom:1px solid var(--line)}
body::before{content:"";position:fixed;inset:0 0 auto;height:env(safe-area-inset-top,0px);z-index:50;background:var(--bg)}
.nav{display:flex;align-items:center;justify-content:space-between;gap:16px;height:64px}
.brand{display:flex;align-items:center;gap:10px;text-decoration:none;font-family:var(--f-display);font-weight:900;font-size:21px}
.brand .mk{width:36px;height:36px;border-radius:11px;background:var(--brand);color:#fff;display:grid;place-items:center}
.brand .mk svg{width:21px;height:21px}
.brand b{color:var(--brand)}
.navr{display:flex;align-items:center;gap:8px}
.iconbtn{width:40px;height:40px;border-radius:12px;border:1.5px solid var(--line);background:var(--bg);color:var(--ink);display:grid;place-items:center;cursor:pointer}
.iconbtn:hover{border-color:var(--brand)}
.iconbtn svg{width:18px;height:18px}

/* breadcrumbs */
.crumbs{display:flex;flex-wrap:wrap;align-items:center;gap:6px 8px;font-size:13px;font-weight:600;color:var(--ink-soft)}
.crumbs a{text-decoration:none}.crumbs a:hover{color:var(--brand)}
.crumbs .sep{opacity:.5}.crumbs .cur{color:var(--ink)}

/* ===== home: hero (always dark, in both themes) ===== */
.lede{font-size:17px;color:var(--ink-soft);max-width:62ch;margin-top:16px}
.hero{position:relative;overflow:hidden;color:#fff;background:radial-gradient(900px 480px at 85% 0%,var(--hg1,rgba(76,110,255,.40)),transparent 60%),radial-gradient(560px 380px at 0% 100%,var(--hg2,rgba(255,92,120,.18)),transparent 60%),var(--hbg,#0a1030);border-radius:0 0 clamp(28px,5vw,56px) clamp(28px,5vw,56px);padding-block:clamp(40px,6vw,84px) clamp(48px,7vw,96px)}
.hero::before{content:"";position:absolute;inset:0;background-image:radial-gradient(rgba(255,255,255,.08) 1px,transparent 1.5px);background-size:28px 28px;-webkit-mask-image:linear-gradient(180deg,#000,transparent 85%);mask-image:linear-gradient(180deg,#000,transparent 85%);pointer-events:none}
.heroin{position:relative;display:grid;grid-template-columns:minmax(0,1.05fr) minmax(0,1fr);gap:clamp(24px,5vw,72px);align-items:center}
.chip-eyebrow{display:inline-flex;align-items:center;gap:8px;font-size:12px;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:#bfe9ff;background:rgba(255,255,255,.08);border:1px solid rgba(255,255,255,.14);padding:7px 14px;border-radius:999px}
.chip-eyebrow i{width:7px;height:7px;border-radius:50%;background:var(--cta,#3bd9f2);box-shadow:0 0 0 4px rgba(255,255,255,.14)}
.hero h1{font-size:clamp(34px,5.2vw,56px);line-height:1.04;margin-top:22px;max-width:11ch}
.hero h1 em{font-style:normal;background:linear-gradient(90deg,var(--em1,#5ef2ff),var(--em2,#9a86ff));-webkit-background-clip:text;background-clip:text;color:transparent}
.hero .lede{color:#b9c6e6;font-size:17px;max-width:42ch;margin-top:20px}
.cta{display:flex;flex-wrap:wrap;gap:14px;margin-top:32px}
.btn-lg{display:inline-flex;align-items:center;justify-content:center;gap:8px;min-height:50px;padding:0 26px;border-radius:999px;font-weight:700;font-size:15px;text-decoration:none;font-family:var(--f-body);transition:background .15s,border-color .15s}
.btn-glow{background:var(--cta,#3bd9f2);color:#041b24;box-shadow:0 10px 30px -10px var(--cta,#3bd9f2)}
.btn-glow:hover{filter:brightness(1.12)}
.btn-ghost{color:#fff;border:1.5px solid rgba(255,255,255,.3)}
.btn-ghost:hover{border-color:#fff;background:rgba(255,255,255,.07)}
.hero :focus-visible{outline-color:var(--cta,#3bd9f2)}
.chips{display:flex;flex-wrap:wrap;gap:10px;margin-top:36px}
.chips span{font-size:13px;font-weight:600;color:#dbe5ff;background:rgba(255,255,255,.07);border:1px solid rgba(255,255,255,.1);padding:8px 14px;border-radius:999px}
.chips b{font-family:var(--f-display);font-weight:900;color:#fff;margin-right:5px}
.heroart{width:100%;max-width:520px;height:auto;justify-self:end;overflow:visible}
.heroart .spin{transform-origin:200px 150px;animation:spin 40s linear infinite}
.heroart .ball{offset-path:path("M170 350 Q235 215 300 350 Q340 280 380 350");offset-rotate:0deg;animation:hop 3.8s ease-in-out infinite}
.heroart .float{animation:float 4.2s ease-in-out infinite}
.heroart .flame{transform-origin:0 22px;animation:flick .5s ease-in-out infinite alternate}
.heroart .tw{transform-box:fill-box;transform-origin:center;animation:tw 3s ease-in-out infinite}
.heroart .cl{transform-origin:62px 262px;animation:cradleL 2.8s ease-in-out infinite}
.heroart .cr{transform-origin:118px 262px;animation:cradleR 2.8s ease-in-out infinite}
@keyframes spin{to{transform:rotate(360deg)}}
@keyframes hop{from{offset-distance:0%}to{offset-distance:100%}}
@keyframes float{50%{transform:translateY(-9px)}}
@keyframes flick{to{transform:scaleY(1.35)}}
@keyframes tw{50%{opacity:.2;transform:scale(.55)}}
@keyframes cradleL{0%{transform:rotate(-32deg)}25%,75%{transform:rotate(0)}100%{transform:rotate(-32deg)}}
@keyframes cradleR{0%,25%{transform:rotate(0)}50%{transform:rotate(32deg)}75%,100%{transform:rotate(0)}}
@media(prefers-reduced-motion:reduce){.heroart *,.livefig *{animation:none!important}}
@media(max-width:860px){.heroin{grid-template-columns:1fr}.hero h1{max-width:14ch}.heroart{max-width:380px;justify-self:center;margin-top:8px}}

/* ===== home: live model band ===== */
.livewrap{padding-block:clamp(48px,6vw,88px) 0}
.live{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1.1fr);gap:clamp(24px,4vw,56px);align-items:center;background:var(--soft);border:1px solid var(--line);border-radius:32px;padding:clamp(24px,4vw,48px)}
.live h2{font-size:clamp(22px,3vw,30px)}
.live p{color:var(--ink-soft);margin-top:12px;max-width:44ch}
.live .btn-lg{margin-top:24px;background:var(--brand);color:#fff}
:root[data-theme="dark"] .live .btn-lg{color:#06121f}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]) .live .btn-lg{color:#06121f}}
.livefig{width:100%;height:auto;border-radius:20px;background:var(--card);border:1px solid var(--line)}
.livefig .gball{offset-path:path("M54 150 Q150 10 246 150");offset-rotate:0deg;animation:hop 3s ease-in-out infinite}
.livefig .ground{stroke:var(--line);stroke-width:2}
.livefig .arc{fill:none;stroke:var(--brand);stroke-width:2.5;stroke-dasharray:2 7;stroke-linecap:round}
.livefig .lt{font-family:var(--f-mono);font-size:11px;fill:var(--ink-soft)}
@media(max-width:860px){.live{grid-template-columns:1fr}}

/* ===== home: pick a topic ===== */
.tools{padding-block:clamp(56px,7vw,96px) 12px}
.tools h2{font-size:clamp(22px,3vw,30px)}
.tools .sub{color:var(--ink-soft);margin-top:8px}
.toolrow{display:flex;flex-wrap:wrap;gap:16px;align-items:center;margin-top:28px}
.search{display:flex;align-items:center;gap:12px;background:var(--card);border:1.5px solid var(--line);border-radius:999px;padding:0 20px;height:54px;flex:1 1 300px;max-width:520px}
.search:focus-within{border-color:var(--brand)}
.search svg{width:18px;height:18px;color:var(--ink-soft);flex:none}
.search input{flex:1;min-width:0;border:0;background:transparent;font:inherit;font-weight:500;color:var(--ink);outline:none;font-size:16px}
.textbtn{font:inherit;font-size:14px;font-weight:700;color:var(--brand);background:none;border:0;cursor:pointer;padding:12px 6px;min-height:44px}
.textbtn:hover{text-decoration:underline}
.legend{display:flex;flex-wrap:wrap;gap:8px 24px;margin-top:20px;font-size:13px;font-weight:600;color:var(--ink-soft)}
.badge{display:inline-flex;align-items:center;gap:6px;font-size:11px;font-weight:700;letter-spacing:.08em;text-transform:uppercase;padding:4px 10px;border-radius:999px;background:var(--ct,var(--brand-t));color:var(--c,var(--brand))}
.badge.soon{background:var(--soft);color:var(--ink-soft)}

/* ===== home: section dropdowns (open by default) ===== */
.branch{padding-block:clamp(16px,2.5vw,28px)}
.branch>summary{list-style:none;cursor:pointer;display:block;-webkit-tap-highlight-color:transparent}
.branch>summary::-webkit-details-marker{display:none}
.sumrow{position:relative;display:flex;gap:20px;align-items:center;background:var(--bn);color:var(--bt);border-radius:28px;padding:clamp(20px,3vw,32px);overflow:hidden;transition:transform .15s}
.branch>summary:hover .sumrow{transform:translateY(-2px)}
.bnum{width:48px;height:48px;border-radius:16px;background:var(--bnn);display:grid;place-items:center;font-family:var(--f-display);font-weight:900;font-size:21px;flex:none;position:relative}
.btext{flex:1;min-width:0;position:relative}
.btext h2{font-size:clamp(20px,2.4vw,26px)}
.btext p{margin-top:4px;font-size:14px;opacity:.88;max-width:62ch}
.bcount{font-size:12px;font-weight:700;white-space:nowrap;opacity:.9;position:relative}
.chev{width:40px;height:40px;border-radius:50%;background:var(--bnn);display:grid;place-items:center;flex:none;transition:transform .2s;position:relative}
.chev svg{width:16px;height:16px}
.branch[open]>summary .chev{transform:rotate(180deg)}
.motif{position:absolute;right:190px;top:50%;transform:translateY(-50%) rotate(-10deg);width:132px;height:132px;opacity:.14;pointer-events:none}
.motif svg{width:100%;height:100%}
.bbody{padding-bottom:clamp(24px,4vw,48px)}
@media(max-width:860px){.motif{display:none}}
@media(max-width:640px){.bcount{display:none}.sumrow{gap:14px;border-radius:24px}.bnum{width:42px;height:42px;border-radius:14px;font-size:18px}}

/* ===== home: topic cards ===== */
.tgrid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:24px;margin-top:28px}
.tcard{display:flex;flex-direction:column;gap:18px;text-decoration:none;background:var(--card);border:1px solid var(--line);border-radius:26px;padding:12px 12px 22px;min-width:0;transition:border-color .15s,transform .15s,box-shadow .15s}
.tcard:hover{border-color:var(--c);transform:translateY(-4px);box-shadow:0 20px 36px -24px var(--c)}
.tcard[hidden]{display:none}
.tart{position:relative;height:108px;border-radius:18px;background:var(--ct);display:grid;place-items:center;overflow:hidden}
.tart::before,.tart::after{content:"";position:absolute;border-radius:50%;background:var(--c);opacity:.13}
.tart::before{width:130px;height:130px;right:-34px;top:-52px}
.tart::after{width:74px;height:74px;left:-22px;bottom:-34px}
.tart .big{position:relative;width:60px;height:60px;border-radius:20px;background:var(--cd);color:var(--cdi);display:grid;place-items:center;box-shadow:0 12px 22px -12px var(--c);transition:transform .2s}
.tcard:hover .big{transform:rotate(-6deg) scale(1.06)}
.tart .big svg{width:30px;height:30px}
.tart .badge{position:absolute;top:10px;right:10px;background:var(--bg)}
.tbody{padding:0 12px;display:flex;flex-direction:column;gap:12px;flex:1}
.tcard small{display:block;font-size:11px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--c)}
.tcard h3{font-size:18px;line-height:1.25;margin-top:4px}
.tcard .prev{font-size:13px;color:var(--ink-soft);line-height:1.6;display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}
.tcard .meta{margin-top:auto;display:flex;justify-content:space-between;align-items:center;gap:10px;padding-top:4px;font-size:13px;font-weight:600;color:var(--ink-soft)}
.tcard .meta .go{color:var(--c);font-weight:700}
.tcard.is-soon .big{opacity:.78}
.noresults{margin-top:48px;text-align:center;color:var(--ink-soft);font-weight:600}
@media(max-width:1020px){.tgrid{grid-template-columns:repeat(2,minmax(0,1fr))}}
@media(max-width:620px){.tgrid{grid-template-columns:1fr;gap:18px}.wrap{padding-left:max(20px,env(safe-area-inset-left,0px));padding-right:max(20px,env(safe-area-inset-right,0px))}}

/* page heads */
.phead{background:linear-gradient(180deg,var(--ct) 0%,var(--bg) 100%);padding-block:28px clamp(28px,4vw,44px)}
.phead .crumbs{margin-bottom:28px}
.ptitle{display:flex;gap:16px;align-items:center}
.ptitle .disc{width:52px;height:52px}.ptitle .disc svg{width:26px;height:26px}
.ptitle h1{font-size:clamp(24px,3vw,32px)}
.ptitle small{display:block;font-size:12px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--c);margin-bottom:4px}
.pbody{padding-block:clamp(32px,5vw,56px) clamp(56px,8vw,96px)}
.bar{height:8px;border-radius:99px;background:var(--line);overflow:hidden;max-width:360px;margin-top:16px}
.bar i{display:block;height:100%;background:var(--c);border-radius:99px}
.barlabel{font-size:13px;font-weight:600;color:var(--ink-soft);margin-top:8px}
.startrow{display:flex;gap:12px;flex-wrap:wrap;margin-top:24px}

/* course outline list (topic page) */
.lessons{list-style:none;margin:0;padding:0;display:grid;gap:12px;max-width:760px}
.lessons a{display:flex;align-items:center;gap:16px;text-decoration:none;background:var(--card);border:1px solid var(--line);border-radius:18px;padding:16px 20px}
.lessons a:hover{border-color:var(--c)}
.lessons .n{width:32px;height:32px;border-radius:50%;background:var(--ct);color:var(--c);display:grid;place-items:center;font-family:var(--f-display);font-weight:900;font-size:14px;flex:none}
.lessons .done .n{background:var(--c);color:var(--cdi)}
.lessons .t{font-weight:600;font-size:15px;min-width:0;flex:1}
.lessons .m{font-size:12px;font-weight:700;color:var(--ink-soft);white-space:nowrap}
.lessons .soonrow{opacity:.7}

/* lesson page */
.course{display:grid;grid-template-columns:272px minmax(0,1fr);gap:48px;align-items:start}
.outline{position:sticky;top:88px;max-height:calc(100vh - 112px);overflow:auto;padding-right:4px}
.outline h2{font-size:15px;margin-bottom:4px}
.outline .sub{font-size:12px;font-weight:600;color:var(--ink-soft);margin-bottom:12px}
.outline ol{list-style:none;margin:0;padding:0;display:grid;gap:2px}
.outline a{display:flex;gap:10px;align-items:flex-start;text-decoration:none;font-size:13.5px;line-height:1.4;padding:8px 10px;border-radius:10px;color:var(--ink-soft);font-weight:500}
.outline a:hover{background:var(--ct);color:var(--ink)}
.outline a.cur{background:var(--ct);color:var(--ink);font-weight:700}
.outline .n{flex:none;width:22px;height:22px;border-radius:50%;border:1.5px solid var(--line);display:grid;place-items:center;font-size:11px;font-weight:700;margin-top:-1px}
.outline .done .n{background:var(--c);border-color:var(--c);color:var(--cdi)}
.outline .cur .n{border-color:var(--c);color:var(--c)}
.outline .done.cur .n{color:var(--cdi)}
.outline .soonrow{opacity:.65}
.outline details{display:contents}
.outmobile{display:none}
@media(max-width:900px){
  .course{grid-template-columns:1fr;gap:24px}
  .outline{display:none}
  .outmobile{display:block;background:var(--soft);border-radius:16px;padding:4px 16px}
  .outmobile summary{cursor:pointer;font-weight:700;font-size:14px;padding:12px 0;list-style:none}
  .outmobile summary::-webkit-details-marker{display:none}
  .outmobile ol{list-style:none;margin:0;padding:0 0 12px;display:grid;gap:2px}
  .outmobile a{display:flex;gap:10px;text-decoration:none;font-size:14px;padding:8px 4px;color:var(--ink-soft)}
  .outmobile a.cur{color:var(--ink);font-weight:700}
  .outmobile .n{flex:none;width:22px;height:22px;border-radius:50%;border:1.5px solid var(--line);display:grid;place-items:center;font-size:11px;font-weight:700}
  .outmobile .done .n{background:var(--c);border-color:var(--c);color:var(--cdi)}
}
.lesson h1{font-size:clamp(24px,3vw,32px)}
.lesson section{margin-top:40px}
.lesson h2{font-size:18px;margin-bottom:16px;display:flex;align-items:center;gap:10px}
.lesson h2::before{content:"";width:6px;height:20px;border-radius:3px;background:var(--c)}
.keyidea{margin-top:20px;background:var(--ct);border-radius:18px;padding:18px 22px;font-size:16px;font-weight:600;max-width:760px}
.keyidea small{display:block;font-size:11px;font-weight:700;letter-spacing:.14em;text-transform:uppercase;color:var(--c);margin-bottom:6px}
.steps{list-style:none;margin:0;padding:0;display:grid;gap:20px;max-width:720px;counter-reset:s}
.steps li{display:grid;grid-template-columns:32px 1fr;gap:14px;counter-increment:s}
.steps li::before{content:counter(s);width:28px;height:28px;border-radius:50%;background:var(--c);color:var(--cdi);display:grid;place-items:center;font-family:var(--f-display);font-weight:900;font-size:14px;margin-top:1px}
.steps h3{font-size:16px;margin-bottom:4px}
.steps p{color:var(--ink-soft);font-size:15px}
.try{margin-top:24px;max-width:720px}
.try h3{font-size:15px;margin-bottom:10px}
.try ul{margin:0;padding:0;list-style:none;display:grid;gap:8px}
.try li{position:relative;padding-left:22px;font-size:15px;color:var(--ink-soft)}
.try li::before{content:"";position:absolute;left:0;top:.62em;width:9px;height:9px;border-radius:50%;border:2px solid var(--c)}
.quiz{max-width:720px}
.quiz .q{font-weight:700;font-size:16px;margin-bottom:14px}
.opts{display:grid;gap:10px}
.opt{font:inherit;font-size:15px;font-weight:500;text-align:left;padding:14px 18px;border-radius:14px;border:1.5px solid var(--line);background:var(--card);color:var(--ink);cursor:pointer}
.opt:hover{border-color:var(--c)}
.opt.bad{border-color:var(--red);background:var(--red-t)}
.opt.good{border-color:var(--green);background:var(--green-t)}
.opt[disabled]{cursor:default}
.fb{margin-top:14px;font-size:15px;color:var(--ink-soft);min-height:1.5em}
.fb b{color:var(--ink)}
.lnav{display:flex;justify-content:space-between;gap:16px;flex-wrap:wrap;margin-top:56px;padding-top:28px;border-top:1px solid var(--line)}
.lnav a{text-decoration:none;display:flex;flex-direction:column;gap:2px;max-width:48%;min-width:0}
.lnav small{font-size:11px;font-weight:700;letter-spacing:.12em;text-transform:uppercase;color:var(--ink-soft)}
.lnav span{font-family:var(--f-display);font-weight:800;font-size:16px}
.lnav a:hover span{color:var(--brand)}
.lnav .r{text-align:right;margin-left:auto}
.empty{background:var(--soft);border-radius:24px;padding:clamp(24px,4vw,40px);max-width:640px}
.empty h3{font-size:19px;margin-bottom:8px}
.empty p{color:var(--ink-soft);font-size:15px}
.btn{display:inline-block;text-decoration:none;font-weight:700;font-size:14px;padding:12px 24px;border-radius:999px;background:var(--brand);color:#fff;border:0;cursor:pointer;font-family:var(--f-body)}
.btn:hover{filter:brightness(.95)}
.btn.ghost{background:transparent;color:var(--brand);border:1.5px solid var(--line)}
.btn.ghost:hover{border-color:var(--brand)}
.btn.small{padding:9px 18px;font-size:13px}
.btn[aria-pressed="true"]{background:var(--ink);color:var(--bg)}

/* interactive models */
.model{margin-top:4px}
.stage{background:var(--soft);border:1px solid var(--line);border-radius:22px;padding:clamp(10px,1.6vw,18px);display:grid;gap:12px}
.stage svg{width:100%;height:auto;touch-action:pan-y}
.graphs{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:12px}
.graphs.one{grid-template-columns:minmax(0,560px)}
.split{display:grid;grid-template-columns:minmax(0,300px) minmax(0,1fr);gap:16px;align-items:start}
.split .graphs{grid-template-columns:minmax(0,1fr)}
@media(max-width:760px){.split{grid-template-columns:1fr}}
.panel{display:grid;grid-template-columns:repeat(auto-fit,minmax(220px,1fr));gap:14px;margin-top:14px}
.ctl{background:var(--card);border:1px solid var(--line);border-radius:16px;padding:14px 16px;display:grid;gap:8px;min-width:0}
.ctl label{display:flex;justify-content:space-between;gap:12px;font-size:13px;font-weight:700}
.ctl output{font-family:var(--f-mono);color:var(--brand);font-weight:700}
.ctl input[type=range]{width:100%;accent-color:var(--brand)}
.ctl select{font:inherit;font-weight:600;font-size:14px;padding:10px 12px;border-radius:10px;border:1.5px solid var(--line);background:var(--bg);color:var(--ink);width:100%}
.actions{display:flex;gap:10px;flex-wrap:wrap;margin-top:14px}
.readouts{display:grid;grid-template-columns:repeat(auto-fit,minmax(160px,1fr));gap:12px;margin-top:14px}
.ro{background:var(--brand-t);border-radius:14px;padding:12px 16px;min-width:0}
.ro small{display:block;font-size:11px;font-weight:700;letter-spacing:.1em;text-transform:uppercase;color:var(--ink-soft)}
.ro b{font-family:var(--f-mono);font-size:16px;color:var(--brand);overflow-wrap:anywhere}
.ro.live{background:var(--card);border:1px solid var(--line)}
.ro.live b{color:var(--ink)}
.eqs{margin-top:14px;background:var(--card);border:1px solid var(--line);border-radius:16px;padding:14px 18px;font-family:var(--f-mono);font-size:13px;line-height:1.9;overflow-x:auto}
.eqs div{white-space:nowrap}
.eqs .ok{color:var(--green);font-weight:700}
.note{margin-top:16px;background:var(--yellow-t);border-radius:16px;padding:14px 18px;font-size:14px;max-width:720px}
.note code,.keyidea code{font-family:var(--f-mono);font-size:13px}

/* svg parts used by models */
.g-grid{stroke:var(--line);stroke-width:1}
.g-axis{stroke:var(--ink-soft);stroke-width:1.5}
.g-text{fill:var(--ink-soft);font-family:var(--f-mono);font-size:11px}
.g-label{fill:var(--ink);font-family:var(--f-body);font-size:12px;font-weight:700}
.g-note{fill:var(--ink);font-family:var(--f-mono);font-size:12px;font-weight:700}
.g-faint{fill:none;stroke:var(--brand);stroke-width:2;stroke-dasharray:4 5;opacity:.4}
.g-curve{fill:none;stroke:var(--brand);stroke-width:3;stroke-linecap:round;stroke-linejoin:round}
.g-area{fill:var(--brand);opacity:.2}
.g-dot{fill:var(--red);stroke:var(--card);stroke-width:2}
.g-tan{fill:none;stroke:var(--green);stroke-width:2.5;stroke-linecap:round}
.road{fill:var(--line)}
.roadmark{stroke:var(--bg);stroke-width:3;stroke-dasharray:14 14}
.tick{stroke:var(--ink-soft);stroke-width:1.5}
.car-body{fill:var(--brand)}
.car2-body{fill:var(--red)}
.car-win{fill:var(--bg);opacity:.85}
.car-wheel{fill:var(--ink)}
.strobe{fill:var(--bg);stroke:var(--ink-soft);stroke-width:2}
.flag{stroke:var(--ink-soft);stroke-width:2}
.ar-v{stroke:var(--green);fill:var(--green)}
.ar-a{stroke:var(--red);fill:var(--red)}
.ar-b{stroke:var(--brand);fill:var(--brand)}
.ar-line{stroke-width:4;stroke-linecap:round}
.ar-dash{stroke-width:3;stroke-dasharray:6 6;stroke-linecap:round;opacity:.8}
.ar-thin{stroke-width:3;stroke-linecap:round}
.handle{fill:var(--card);stroke:var(--ink);stroke-width:3;cursor:grab;touch-action:none}
.handle:active{cursor:grabbing}
.sv-ground{fill:var(--soft);stroke:var(--line);stroke-width:2}
.ground{fill:var(--line)}
.ball{fill:var(--red)}
.ball2{fill:var(--ink)}
.trail{fill:none;stroke:var(--brand);stroke-width:3.5;stroke-linecap:round;stroke-linejoin:round}
.pred{fill:none;stroke:var(--brand);stroke-width:2.5;stroke-dasharray:6 7;opacity:.55}
.peak{stroke:var(--green);stroke-width:2;stroke-dasharray:4 5}
.svg-title{fill:var(--ink);font-family:var(--f-body);font-size:13px;font-weight:700}
.tree{fill:var(--green);opacity:.8}
.trunk{fill:var(--ink-soft)}
.wave{fill:none;stroke:var(--brand);stroke-width:3.5;stroke-linecap:round;stroke-linejoin:round}
.crest{fill:var(--red)}
.coil{fill:none;stroke:var(--ink);stroke-width:3;stroke-linejoin:round;stroke-linecap:round}
.mass{fill:var(--brand)}
.massbox{fill:var(--brand)}
.wire{fill:none;stroke:var(--ink);stroke-width:3;stroke-linejoin:round}
.cyl{fill:none;stroke:var(--ink-soft);stroke-width:4;stroke-linejoin:round}
.lid{fill:var(--ink)}
.gasdot{fill:var(--brand)}

/* footer */
footer.foot{background:var(--navy);color:#c9d7ea;padding-block:40px}
:root[data-theme="dark"] footer.foot{background:#071426}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]) footer.foot{background:#071426}}
.footin{display:flex;justify-content:space-between;gap:24px;flex-wrap:wrap;font-size:14px}
.footin .b{font-family:var(--f-display);font-weight:900;font-size:19px;color:#fff;display:block;margin-bottom:4px}
@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}.chev,.tcard{transition:none}}

.foot .priv{border-top:1px solid rgba(255,255,255,.14);margin-top:28px;padding-top:20px;font-size:13px;line-height:1.7;color:#aebfd8;max-width:80ch}
.foot .priv a{color:#fff;font-weight:700}
.foot .flinks{display:flex;gap:18px;flex-wrap:wrap;margin-top:6px}
.foot .flinks a{color:#fff;text-decoration:none;font-weight:600}.foot .flinks a:hover{text-decoration:underline}

/* privacy notice */
.prose{max-width:68ch}
.prose h2{font-size:20px;margin:40px 0 10px}
.prose p{color:var(--ink-soft);margin-top:10px}
.prose a{color:var(--brand);font-weight:600}
.callout{background:var(--brand-t);border-left:5px solid var(--brand);border-radius:16px;padding:20px 24px;color:var(--ink);font-size:15px}
.callout b{font-family:var(--f-display)}

/* touch comfort: bigger slider handles and tap areas on all screens */
.ctl input[type=range]{height:36px;background:transparent;cursor:pointer;touch-action:pan-y}
.ctl input[type=range]::-webkit-slider-thumb{width:26px;height:26px}
.ctl input[type=range]::-moz-range-thumb{width:26px;height:26px}
.crumbs a{display:inline-flex;align-items:center;min-height:40px}
.foot .flinks a{display:inline-flex;align-items:center;min-height:44px}
.foot .priv a{display:inline-block;padding-block:10px;margin-block:-10px}
@media(max-width:480px){.btn-lg{padding:0 22px}.cta{gap:10px}}
.livefig{max-width:520px;justify-self:center}

/* main navigation: Home, Topics (sections > topics), links to sister sites */
.nav{position:relative}
.navr{margin-left:auto}
.mainnav{display:flex;align-items:center;gap:4px;margin-left:24px;flex:1}
.nl{display:inline-flex;align-items:center;gap:6px;font:inherit;font-size:14px;font-weight:600;color:var(--ink-soft);text-decoration:none;background:none;border:0;cursor:pointer;padding:0 14px;min-height:44px;border-radius:999px;white-space:nowrap}
.nl:hover,.nl[aria-expanded="true"],.nl[aria-current]{color:var(--brand);background:var(--brand-t)}
.nl svg{width:14px;height:14px;flex:none;transition:transform .2s}
.nl[aria-expanded="true"] svg{transform:rotate(180deg)}
.nl.ext svg{width:13px;height:13px;opacity:.7;transform:none}
.nsep{width:1px;height:22px;background:var(--line);margin:0 8px}
.dd{position:static}
.mega{position:absolute;top:calc(100% + 8px);left:24px;width:min(820px,calc(100% - 48px));background:var(--card);border:1px solid var(--line);border-radius:24px;box-shadow:0 30px 60px -30px rgba(10,16,48,.4);padding:12px;z-index:60}
.mega[hidden]{display:none}
.msec{list-style:none;margin:0;padding:0;width:268px;display:flex;flex-direction:column;gap:2px}
.msb{width:100%;display:flex;align-items:center;gap:12px;font:inherit;font-size:15px;font-weight:700;color:var(--ink);background:none;border:0;border-radius:14px;padding:0 14px;min-height:48px;cursor:pointer;text-align:left}
.msb span{flex:1}
.msb small{font-size:12px;font-weight:700;color:var(--ink-soft)}
.msb svg{display:none;width:16px;height:16px;flex:none}
.msi.act .msb{background:var(--ct)}
.dot{width:12px;height:12px;border-radius:50%;background:var(--bn);flex:none}
.mt{display:none;position:absolute;top:12px;left:296px;right:12px;bottom:12px;overflow:auto}
.msi.act .mt{display:block}
.mall{display:inline-flex;align-items:center;min-height:40px;font-size:14px;font-weight:700;color:var(--c);text-decoration:none;margin-bottom:6px;padding:0 12px}
.mt ul{list-style:none;margin:0;padding:0;display:grid;grid-template-columns:1fr 1fr;gap:2px 16px}
.mt li a{display:flex;align-items:center;min-height:44px;padding:0 12px;border-radius:12px;font-size:14px;font-weight:600;color:var(--ink);text-decoration:none}
.mt li a:hover{background:var(--ct);color:var(--c)}
.burger{display:none}
body.navlock{overflow:hidden}
@media(max-width:960px){
  .burger{display:grid}
  .mainnav{display:none;position:fixed;top:calc(64px + env(safe-area-inset-top,0px));left:0;right:0;bottom:0;margin:0;padding:12px 20px 56px;background:var(--bg);flex-direction:column;align-items:stretch;gap:2px;overflow:auto;z-index:45}
  .mainnav.open{display:flex}
  .nl{justify-content:space-between;font-size:17px;padding:0 16px;min-height:52px;border-radius:14px;width:100%}
  .nsep{width:auto;height:1px;margin:10px 0}
  .mega{position:static;width:auto;box-shadow:none;border:0;padding:4px 0 8px;background:transparent}
  .msec{width:auto}
  .msb svg{display:block}
  .msi.act .msb svg{transform:rotate(180deg)}
  .mt{position:static;padding:4px 0 10px 28px}
  .mt ul{grid-template-columns:1fr}
}