:root{color-scheme:light;--bg:#edf1f5;--paper:#fff;--ink:#152938;--muted:#526574;--line:#d9e2e8;--green:#087f63;--mint:#75efc7;--blue:#245fc5;--navy:#102637}*{box-sizing:border-box}body{margin:0;background:var(--bg);color:var(--ink);font:16px/1.6 -apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif}a{color:var(--blue)}button,input,summary{font:inherit}a:focus-visible,summary:focus-visible,button:focus-visible,input:focus-visible{outline:3px solid var(--blue);outline-offset:5px}h1,h2,h3,p{margin:0}.shell{max-width:1440px;padding:25px 34px 30px;margin:auto}.site-header{display:flex;align-items:center;gap:30px;justify-content:space-between;margin-bottom:26px}.site-brand{display:inline-flex;align-items:center;gap:12px;color:var(--ink);text-decoration:none;letter-spacing:.12em;font-size:14px;font-weight:800;white-space:nowrap}.site-brand span{display:grid;place-items:center;border-radius:9px;width:35px;height:35px;background:var(--ink);color:var(--mint);font-size:25px;line-height:1}.site-nav{display:flex;align-items:center;gap:24px;flex-wrap:wrap;font-size:14px}.site-nav>a{text-decoration:none;color:var(--muted)}.site-nav>a[aria-current=page]{color:var(--ink);font-weight:700}.language-menu,.games-menu{position:relative;z-index:10}.language-menu summary,.games-menu summary{cursor:pointer;padding:8px 12px;border:1px solid #bccbd6;border-radius:8px;font-size:14px}.language-menu nav,.games-menu nav{position:absolute;inset-inline-end:0;top:100%;width:215px;display:grid;padding:8px;margin-top:8px;background:#fff;border:1px solid var(--line);border-radius:10px;box-shadow:0 10px 24px #10263720}.language-menu nav a,.games-menu nav a{display:block;padding:7px 12px;text-decoration:none;border-radius:5px}.language-menu nav a:hover,.language-menu nav a[aria-current=page],.games-menu nav a:hover,.games-menu nav a[aria-current=page]{background:#e2f2ec;color:#08694f}.skip-link{position:absolute;inset-inline-start:16px;top:-100px;z-index:20;background:white;padding:12px}.skip-link:focus{top:12px}.home-hero{background:var(--navy);color:#f2f8fc;border-radius:20px;padding:clamp(26px,5vw,64px);display:grid;grid-template-columns:1.3fr 1fr;gap:40px;align-items:end}.eyebrow-label{font-size:14px;font-weight:700;letter-spacing:.11em;text-transform:uppercase}.home-hero .eyebrow-label{color:var(--mint);margin-bottom:20px}.home-hero h1{font-size:clamp(34px,4.3vw,62px);line-height:1.08;letter-spacing:-.05em;max-width:860px}.home-hero p:last-child{color:#bdd0dd;font-size:18px;max-width:360px;border-inline-start:2px solid var(--mint);padding-inline-start:22px}.collection{padding-top:38px}.collection-header{display:flex;justify-content:space-between;align-items:center;gap:20px;margin-bottom:18px}.collection-header h2{font-size:24px;letter-spacing:-.035em}.collection-header span{font-size:14px;color:var(--muted)}.game-card{display:grid;grid-template-columns:1fr 1fr;background:white;border:1px solid var(--line);border-radius:18px;overflow:hidden}.game-card-copy{padding:32px}.game-card .eyebrow-label{color:var(--green)}.game-card .game-card-title{font-size:32px;line-height:1.2;letter-spacing:-.04em;margin:13px 0}.game-card-copy>p:not(.eyebrow-label){color:var(--muted);max-width:560px}.game-types{display:flex;gap:10px;flex-wrap:wrap;margin:22px 0}.game-types span{font-size:14px;background:#edf2f6;border-radius:6px;padding:5px 10px}.play-link{display:inline-flex;gap:24px;justify-content:space-between;align-items:center;background:var(--green);border-radius:9px;padding:12px 18px;color:#fff;text-decoration:none;font-weight:650}.play-link:hover{background:#05664f}.equation-board{margin:16px;background:#102637;color:#f4f8fb;border-radius:12px;display:flex;flex-direction:column;justify-content:center;gap:20px;padding:clamp(24px,4vw,48px)}.equation-board>div{padding-bottom:20px;border-bottom:1px solid #355162}.equation-board>div:last-child{padding:0;border:0}.equation-board dt{font-size:14px;color:#bcd0df;margin-bottom:9px}.equation-board dd{margin:0;font:clamp(24px,2.6vw,38px)/1.4 ui-monospace,SFMono-Regular,PhisicosArabic,monospace;color:var(--mint)}.equation-board>div:last-child dd{color:#8bc6ff}.coming-next{margin-top:18px;padding:23px 26px;border:1px dashed #b5c5d1;border-radius:12px;display:flex;justify-content:space-between;align-items:baseline;gap:30px}.coming-next h3{font-size:16px;font-weight:650}.coming-next p{color:var(--muted);font-size:14px;max-width:590px}.home-learning{padding:38px 0 10px;display:grid;grid-template-columns:1fr 1fr;gap:45px}.home-learning h2{font-size:24px;line-height:1.3;letter-spacing:-.025em;margin-bottom:15px}.home-learning p,.home-learning li{color:var(--muted)}.home-learning ol{margin:0;padding-inline-start:25px;display:grid;gap:16px;align-content:center}.home-learning li{padding-inline-start:8px}.home-learning li::marker{color:var(--green);font-weight:700}.site-footer{margin-top:32px;padding-top:18px;border-top:1px solid #c5d2dc;display:flex;justify-content:space-between;gap:20px;flex-wrap:wrap;color:var(--muted);font-size:14px}.breadcrumbs{margin:0 0 20px;font-size:14px;display:flex;align-items:center;flex-wrap:wrap;gap:10px;color:var(--muted)}.breadcrumbs a{text-decoration:none}.learning-content{margin-top:34px;padding-top:28px;border-top:1px solid #c5d2dc;display:grid;grid-template-columns:1fr 1fr;gap:30px 45px}.learning-content h2{font-size:23px;line-height:1.3;margin-bottom:14px;letter-spacing:-.025em}.learning-content p,.learning-content li{font-size:16px;line-height:1.65;color:var(--muted)}.learning-content ol{padding-inline-start:22px;margin:0}.learning-content li{padding-inline-start:4px;margin-bottom:10px}.learning-content .worked-example{padding:22px;border:1px solid #b7d9ce;background:#e4f3ed;border-radius:12px;margin-top:24px}.worked-example h3{font-size:18px;line-height:1.4;margin-bottom:10px}.faq{grid-column:1/-1}.faq details{border-bottom:1px solid var(--line);padding:15px 0}.faq summary{font-weight:650;cursor:pointer;font-size:16px}.faq details p{margin-top:10px;max-width:85ch}.back-link{font-size:16px;display:inline-block;margin-top:20px}.no-js{padding:20px;background:#fff3d8;border-radius:10px;margin-bottom:16px}.masthead h1{font-size:clamp(27px,3vw,36px);max-width:920px}.concept-tags{flex-wrap:wrap}.metric-label{white-space:normal!important;font-size:14px!important;line-height:1.35}.metric-components{overflow-wrap:anywhere}.scene-subtitle,.hint,.legend,.scene-title,.scene-top .status,.challenge-steps,.explain,.range-ends{font-size:14px}.eyebrow{font-size:14px;letter-spacing:.06em}.scene-top{flex-wrap:wrap}.scene-top>div{min-width:0}.label-row{flex-wrap:wrap}.challenge-body{flex-wrap:wrap}.challenge button{white-space:normal}.challenge-top{flex-wrap:wrap}.lab-tabs button{white-space:normal;min-width:0}.arcade-score{grid-template-columns:repeat(3,minmax(0,1fr))}.canvas-caption{right:16px;line-height:1.35}.chase-live{font-size:14px}.chase-live span{min-width:0}.chase-live output{font-size:12px}html{scroll-behavior:smooth}[id]{scroll-margin-top:18px}@media(max-width:1000px){.site-header{align-items:flex-start}.site-nav{gap:14px;justify-content:flex-end}.home-hero{grid-template-columns:1fr;gap:26px}.home-hero p:last-child{max-width:620px}.game-card-copy{padding:26px}.home-learning{gap:28px}.coming-next{display:block}.coming-next p{margin-top:6px}.concept-tags{display:none}}@media(max-width:760px){.shell{padding:18px 14px 24px}.site-header{gap:15px;flex-wrap:wrap;margin-bottom:20px}.site-nav{width:100%;justify-content:flex-start;gap:12px 20px}.language-menu{margin-inline-start:auto}.site-nav>a{max-width:54%;overflow-wrap:anywhere}.site-brand{font-size:14px}.game-card{grid-template-columns:1fr}.equation-board{margin-top:0}.home-hero{padding:28px 24px;border-radius:14px}.home-hero h1{font-size:clamp(31px,7.5vw,46px)}.home-hero p:last-child{font-size:16px}.collection{padding-top:26px}.collection-header{align-items:flex-start;flex-direction:column;gap:4px}.game-card .game-card-title{font-size:28px}.game-card-copy{padding:24px}.home-learning,.learning-content{grid-template-columns:1fr;gap:28px}.home-learning{padding-top:30px}.site-footer{gap:12px;flex-direction:column}.coming-next{padding:20px}.home-learning h2,.learning-content h2{font-size:22px}.play-link{font-size:16px;width:100%}.scene-top{padding:14px}.instant{font-size:12px}.instant strong{font-size:15px}.canvas-caption{font-size:12px;left:14px}.transport button{min-height:44px}.language-menu summary,.games-menu summary{min-height:42px}.metric-label{font-size:13px!important}.chase-measure-label{font-size:14px}.arcade-scene .scene-title{font-size:14px}}@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}}
.game-card + .game-card{margin-top:20px}
/* Games menu: a quieter trigger than the language menu, highlighted on game pages. */
.games-menu{z-index:11}.games-menu nav{width:250px}.games-menu summary{border-color:transparent;color:var(--muted)}.games-menu[open] summary,.games-menu:has(a[aria-current=page]) summary{color:var(--ink);font-weight:700}
@media(max-width:760px){.games-menu nav{inset-inline-start:0;inset-inline-end:auto}}
.games-menu nav{width:270px;max-height:min(72vh,600px);overflow:auto}.menu-group+.menu-group{border-top:1px solid var(--line);margin-top:6px;padding-top:6px}.games-menu nav a.menu-topic{font-size:12px;font-weight:700;letter-spacing:.08em;text-transform:uppercase;color:var(--green)}.games-menu .menu-group a:not(.menu-topic){padding-inline-start:22px}
.topic-browser{padding-top:38px}.topic-grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(230px,1fr));gap:16px}.topic-tile{background:#fff;border:1px solid var(--line);border-radius:16px;padding:22px;display:flex;flex-direction:column;gap:10px}.topic-tile .eyebrow-label{color:var(--green);font-size:12px}.topic-tile h2,.topic-tile h3{font-size:22px;line-height:1.2;letter-spacing:-.03em}.topic-tile h2 a,.topic-tile h3 a{color:inherit;text-decoration:none}.topic-tile h2 a:hover,.topic-tile h3 a:hover{text-decoration:underline}.topic-tile p:not(.eyebrow-label){color:var(--muted);font-size:15px}.topic-tile ul{list-style:none;margin:auto 0 0;padding:12px 0 0;border-top:1px solid var(--line);display:grid;gap:4px;font-size:14px}.topic-tile li a{display:block;padding:4px 0;color:#08694f;text-decoration:none}.topic-tile li a:hover{text-decoration:underline}
.collection-header a{font-size:14px;font-weight:650;color:#08694f;text-decoration:none;white-space:nowrap}.topic-group+.topic-group{margin-top:32px}.topic-group-header{display:flex;justify-content:space-between;align-items:baseline;gap:16px;margin-bottom:14px}.topic-group-header h3{font-size:20px;letter-spacing:-.02em}.topic-group-header h3 a{color:inherit;text-decoration:none}.topic-group-header h3 a:hover{text-decoration:underline}.topic-group-header span{font-size:14px;color:var(--muted)}.topic-group .game-card+.game-card{margin-top:16px}.game-card h4.game-card-title{font-size:28px}
.topic-hero{background:var(--navy);color:#f2f8fc;border-radius:20px;padding:clamp(24px,4vw,48px)}.topic-hero .eyebrow-label{color:var(--mint);margin-bottom:14px}.topic-hero h1{font-size:clamp(30px,3.6vw,48px);line-height:1.1;letter-spacing:-.045em;max-width:900px}.topic-hero p:last-child{color:#bdd0dd;font-size:18px;max-width:720px;margin-top:16px}.other-topics{padding-top:38px}
.also-in{display:flex;flex-wrap:wrap;align-items:center;gap:8px;margin:-8px 0 20px;font-size:14px;color:var(--muted)}.also-in a{font-weight:650;color:#08694f;text-decoration:none;background:#e4f3ed;border:1px solid #b7d9ce;border-radius:99px;padding:4px 12px}.also-in a:hover{text-decoration:underline}
.tag-lesson{display:grid;grid-template-columns:1fr minmax(0,420px);gap:24px 40px;align-items:center;padding-top:38px}.tag-lesson h2,.tag-guide h2{font-size:24px;letter-spacing:-.035em;margin-bottom:12px}.tag-lesson p{font-size:17px;line-height:1.65;color:var(--muted)}.tag-lesson .equation-board{margin:0}
.tag-guide{padding-top:38px}.tag-guide ol{padding-inline-start:22px;margin:0;display:grid;gap:10px;max-width:900px}.tag-guide li{font-size:16px;line-height:1.6;color:var(--muted)}.tag-guide li a{font-weight:650;color:#08694f}
@media(max-width:760px){.tag-lesson{grid-template-columns:1fr;padding-top:26px}.tag-guide{padding-top:26px}}

/* Japanese headings break between phrases, not inside words, where the browser supports it. */
html:lang(ja) :is(h1,h2,h3){word-break:auto-phrase}

/* Arabic letters in monospace readouts come from a proportional system font so they stay joined; the range leaves Latin text in the monospace face. */
@font-face{font-family:PhisicosArabic;src:local("Geeza Pro"),local("GeezaPro"),local("Segoe UI"),local("Tahoma"),local("Noto Sans Arabic"),local("Noto Naskh Arabic"),local("Arial");unicode-range:U+0600-06FF,U+0750-077F,U+08A0-08FF,U+FB50-FDFF,U+FE70-FEFF}
/* Right-to-left pages mirror the layout. Simulations, number entry, readouts, and equations keep physics' left-to-right axes; direction arrows in links turn to point the reading way. */
[dir=rtl] :is(.canvas-wrap,.lander-stage,.module-stage,canvas,input[type=range],.range-ends,.answer-row,.equation-board dd,.module-equation output,.equation){direction:ltr}
/* Text laid over a simulation takes its direction from its own words, so an Arabic caption reads right to left inside the left-to-right stage. */
[dir=rtl] :is(.canvas-wrap,.lander-stage,.module-stage) *{unicode-bidi:plaintext}
[dir=rtl] :is(.metric-value,.metric-components,.metric-equation,output:not(.module-equation output),.readout strong,.score-card strong,.arcade-score strong){direction:ltr;unicode-bidi:isolate;text-align:right}
[dir=rtl] :is(.play-link,.collection-header a,.back-link) span[aria-hidden]{display:inline-block;transform:scaleX(-1)}
/* Arabic letters join, so spacing between them would break the words apart. */
html:lang(ar) *{letter-spacing:0!important}