:root{--ink:#153747;--muted:#6b818a;--teal:#087f7c;--mint:#84dfc3;--line:#dfe9eb;--paper:#f6f9f8;--nav:#102b3d;font-family:system-ui,-apple-system,BlinkMacSystemFont,"Segoe UI",sans-serif;color:var(--ink);background:var(--paper);font-size:15px}*{box-sizing:border-box}body{margin:0;-webkit-tap-highlight-color:transparent}button,input,a{font:inherit}button,a{touch-action:manipulation}button{cursor:pointer;color:inherit}button:focus-visible,a:focus-visible,input:focus-visible{outline:3px solid #309f96;outline-offset:3px}[hidden]{display:none!important}button{border:0;background:none}button:disabled{opacity:.55;cursor:wait}a{color:inherit;text-decoration:none}button svg,[data-icon] svg{width:22px;height:22px;display:block;stroke-width:1.7}h1,h2,h3,p{margin:0}h2{font-size:18px;font-weight:680;letter-spacing:-.4px}.app-header{display:flex;align-items:center;justify-content:space-between;padding:calc(14px + env(safe-area-inset-top,0px)) 20px 14px;background:#f6f9f8f5;border-bottom:1px solid #e6edec;position:sticky;top:0;z-index:15;backdrop-filter:blur(14px)}.brand{display:flex;gap:10px;align-items:center;font-weight:800;letter-spacing:1px;font-size:18px}.brand img{border-radius:11px}.brand small{display:block;font-size:8px;font-weight:600;letter-spacing:1.6px;color:var(--muted);margin-top:4px}.head-actions{display:flex;gap:9px;align-items:center}.network{width:7px;height:7px;border-radius:50%;background:#44a48b}.network.offline{background:#c3995f}.icon-button{width:44px;height:44px;display:inline-flex;align-items:center;justify-content:center;border-radius:13px;flex-shrink:0}.icon-button:hover{background:#e8f1ef}.icon-button[aria-pressed=true]{color:var(--teal);background:#e2f4ed}.icon-button[aria-pressed=true] svg{fill:#b8e8d7}.home-content{max-width:1040px;margin:auto;padding:20px 20px calc(105px + env(safe-area-inset-bottom,0px))}.hero{border-radius:23px;background:radial-gradient(ellipse at 100% 0,#295561,transparent 80%),var(--nav);color:#effaf6;padding:27px 24px;position:relative;overflow:hidden;display:flex;justify-content:space-between;min-height:238px;isolation:isolate}.eyebrow{display:block;font-size:8px;letter-spacing:1.3px;font-weight:700;color:#8ad9c5}.hero h1{font-size:32px;line-height:1.2;font-weight:730;letter-spacing:-1px;margin:15px 0 12px}.hero p{font-size:12px;line-height:1.65;color:#bcd2d8;max-width:230px}.hero svg{position:absolute;width:155px;height:210px;right:-11px;top:22px;z-index:-1;opacity:.9}.hero-count{font-size:11px;color:#a5c7ce;display:block;margin-top:20px}.hero-count b{color:#e2f8ef;font-weight:650}.section-heading{display:flex;align-items:center;justify-content:space-between;gap:10px;margin:25px 0 15px}.section-heading>span{font-size:11px;color:var(--muted);white-space:nowrap}.grade-grid{display:grid;grid-template-columns:repeat(5,minmax(0,1fr));gap:9px}.grade-card{background:white;border:1px solid var(--line);padding:14px 3px;border-radius:15px;text-align:center;min-height:90px;position:relative}.grade-card strong{font-size:27px;display:block;color:#406876;font-weight:650;letter-spacing:-1px}.grade-card small{font-size:9px;color:var(--muted);display:block;margin-top:4px}.grade-card[aria-pressed=true]{border-color:#79bcb1;background:#e9f6f0;box-shadow:inset 0 0 0 .5px #79bcb1}.grade-card[aria-pressed=true] strong{color:#087e76}.search-wrap{margin:23px 0 5px;background:white;border:1px solid var(--line);border-radius:13px;display:flex;align-items:center;gap:10px;padding:2px 12px;min-height:50px;color:#65828b}.search-wrap>span{flex-shrink:0}.search-wrap input{font-size:16px!important;width:100%;min-width:0;border:0;background:none;outline:none;font-size:14px;padding:13px 0;color:var(--ink)}.search-wrap input::placeholder{color:#8a9ca3}.search-wrap .icon-button{width:32px;height:36px}.chapter-chips{display:flex;gap:8px;overflow-x:auto;padding:0 0 12px;margin-bottom:4px;scrollbar-width:none}.chapter-chip{white-space:nowrap;padding:11px 13px;border-radius:10px;font-size:11px;background:white;border:1px solid var(--line);min-height:40px}.chapter-chip[aria-pressed=true]{color:white;background:#234653;border-color:#234653}.lab-list{display:grid;gap:10px}.lab-card{display:grid;grid-template-columns:minmax(0,1fr) 45px;background:white;border:1px solid var(--line);border-radius:16px;overflow:hidden;min-height:93px}.lab-open{display:flex;text-align:left;align-items:center;gap:13px;padding:16px 3px 16px 13px;min-width:0;width:100%}.lab-open>.lab-symbol{width:47px;height:53px;flex-shrink:0;background:#eef5f4;border:1px solid #e3edeb;display:flex;align-items:center;justify-content:center;border-radius:12px;color:#4a8b87}.lab-symbol svg{width:28px;height:28px}.lab-copy{min-width:0}.lab-meta{display:block;color:#789098;font-size:9px;font-weight:600;letter-spacing:.1px;margin-bottom:6px}.lab-title{display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden;font-size:13px;line-height:1.55;font-weight:650}.lab-status{display:flex;align-items:center;gap:4px;font-size:9px;color:#3e8b75;margin-top:6px}.lab-status svg{width:12px;height:12px}.lab-card>.favorite{align-self:center;width:41px;color:#8ca1a9}.favorite[aria-pressed=true]{background:none;color:#188976}.recent-card{background:#e7f4ed;border-color:#c8e3d8}.recent-card .lab-meta{color:#60958d}.empty{text-align:center;padding:38px 15px;color:var(--muted);border:1px dashed #d1e0df;border-radius:17px;background:#fff}.empty>span{display:inline-flex;color:#82a7a6;margin-bottom:15px}.empty h3{font-size:15px;color:#41616c}.empty p{font-size:12px;line-height:1.7;margin:10px 0}.student-note{font-size:10px;line-height:1.8;color:#8a9ca3;margin:24px 10px 0;text-align:center}.bottom-nav{position:fixed;bottom:0;left:0;right:0;display:flex;padding:8px 15px calc(8px + env(safe-area-inset-bottom,0px));background:#fffffff5;border-top:1px solid #e0e9e7;backdrop-filter:blur(18px);z-index:20}.bottom-nav>button{flex:1;min-height:53px;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:6px;color:#8aa0a6;font-size:10px}.bottom-nav>button[aria-current=page]{color:var(--teal);font-weight:700}.bottom-nav>button[aria-current=page]>span:first-child{background:#e4f5ec;border-radius:9px;padding:3px 18px;margin:-3px -18px}.sheet{border:1px solid #d8e5e3;border-radius:24px 24px 0 0;padding:23px 24px calc(23px + env(safe-area-inset-bottom,0px));color:var(--ink);width:100%;max-width:500px;margin:auto auto 0;max-height:91dvh;overflow:auto;background:#fcfefd;box-shadow:0 -15px 90px #061d3550}.sheet::backdrop{background:#0a243b77;backdrop-filter:blur(3px)}.sheet-header{display:flex;justify-content:space-between;align-items:center;margin-bottom:13px;gap:10px}.sheet-header .eyebrow{color:#619e93;font-size:9px}.sheet h2{font-size:23px;line-height:1.4;letter-spacing:-.6px}.sheet>p{font-size:13px;line-height:1.8;color:var(--muted);margin:12px 0 18px}.main-button,.secondary-button{min-height:49px;padding:13px 16px;border-radius:12px;width:100%;font-size:13px;font-weight:650;margin:9px 0 0;background:var(--teal);color:white}.secondary-button{background:#ecf4f1;color:#477367;border:1px solid #d9e7e1}.apple{background:#163443}.text-button{min-height:44px;color:var(--teal);font-size:12px;padding:12px 5px}.sheet-divider{height:1px;background:var(--line);margin:23px 0 11px}.setting-row{display:flex;align-items:center;text-align:left;gap:13px;min-height:74px;width:100%;border-bottom:1px solid #e9f0ed}.setting-row>span:first-child{background:#eaf3ef;color:#4e9588;padding:12px;border-radius:12px}.setting-row>span:nth-child(2){flex:1}.setting-row b{font-size:13px;display:block}.setting-row small{font-size:10px;line-height:1.6;display:block;color:var(--muted);margin-top:5px}.setting-row>span:last-child{color:#8da39f}.sheet .version-note{text-align:center;font-size:10px;margin:20px 0 0;color:#9aacb0}.sheet .status-note{font-size:11px;line-height:1.8;margin:13px 0 0;color:#5b8479;overflow-wrap:anywhere}.install-icon{border-radius:20px;margin:5px 0 17px}#install-help{font-size:13px;line-height:1.9;color:var(--muted);margin:17px 0}#install-help ol{padding-left:20px}#download-grades{margin-top:16px}.download-row{display:flex;gap:12px;align-items:center;border:1px solid var(--line);border-radius:14px;padding:13px;margin:9px 0;background:white}.download-row strong{font-size:25px;color:#547b84;min-width:34px}.download-row>div{flex:1;font-size:12px}.download-row small{display:block;font-size:10px;color:var(--muted);margin-top:4px}.download-row button{min-width:65px;min-height:42px;background:#e6f4ec;color:var(--teal);border-radius:9px;font-size:11px}.toast{position:fixed;z-index:200;bottom:calc(91px + env(safe-area-inset-bottom,0px));left:50%;transform:translateX(-50%);max-width:calc(100% - 30px);width:max-content;border:1px solid #547f80;background:#143b47;color:#ecf7f2;border-radius:12px;padding:13px 18px;font-size:12px;line-height:1.7;box-shadow:0 8px 30px #0c29352a}.viewer{position:fixed;inset:0;background:#102b3d;display:flex;flex-direction:column;z-index:60;isolation:isolate}.viewer-head{padding:calc(6px + env(safe-area-inset-top,0px)) 9px 6px;min-height:61px;display:flex;align-items:center;gap:8px;border-bottom:1px solid #41616a;color:#d9ede9;background:#143747}.viewer-head>div{flex:1;min-width:0}.viewer-head small{display:block;font-size:9px;color:#87bcb5;margin-bottom:5px}.viewer-head h2{font-size:12px;line-height:1.45;letter-spacing:0;white-space:nowrap;overflow:hidden;text-overflow:ellipsis}.viewer-head .icon-button:hover{background:#24515b}.frame-viewport{flex:1;min-height:0;overflow:auto;position:relative;overscroll-behavior:contain}#lab-frame{border:0;display:block;width:100%;height:100%;background:#102b3d;max-width:none}.viewer-loading{position:absolute;inset:0;background:#102b3d;display:flex;flex-direction:column;align-items:center;justify-content:center;gap:20px;color:#a9ccc9;font-size:12px;pointer-events:none}.spinner{width:27px;height:27px;border:2px solid #315d67;border-top-color:#8de4c8;border-radius:50%;animation:spin .8s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.viewer-tools{display:flex;gap:3px;align-items:center;justify-content:center;padding:7px 5px calc(7px + env(safe-area-inset-bottom,0px));min-height:65px;background:#143747;border-top:1px solid #375963;overflow-x:auto;flex-shrink:0}.viewer-tools button{display:flex;flex:1;min-width:44px;min-height:46px;flex-direction:column;align-items:center;justify-content:center;gap:5px;color:#b5d2cf;font-size:8px;white-space:nowrap;border-radius:8px}.viewer-tools button[aria-pressed=true]{background:#2b5d60;color:#b8f0d9}.viewer-tools svg{width:20px;height:20px}.viewing{overflow:hidden}.viewing .toast{bottom:calc(82px + env(safe-area-inset-bottom,0px))}.immersive .viewer-head{display:none}.immersive .viewer-tools{position:absolute;bottom:calc(10px + env(safe-area-inset-bottom,0px));left:50%;transform:translateX(-50%);padding:5px;border:1px solid #6b8b8f;background:#163c49ee;border-radius:13px;min-height:50px;max-width:calc(100% - 20px);width:auto;gap:7px}.immersive .viewer-tools button{min-width:49px}.immersive .viewer-tools #sim-reset,.immersive .viewer-tools #sim-graphs,.immersive .viewer-tools #rotate{display:none}.immersive .viewer-tools #observe{color:#b4f3d7}.immersive #frame-viewport{padding-bottom:0}
@media(min-width:700px){.hero{padding:32px 40px;min-height:260px}.hero svg{right:45px;width:220px;height:250px}.hero h1{font-size:40px}.hero .eyebrow{font-size:10px}.hero p{font-size:14px;max-width:320px}.grade-card{padding:17px}.grade-card small{font-size:11px}.lab-list{grid-template-columns:repeat(2,minmax(0,1fr))}.lab-title{font-size:14px}.lab-meta{font-size:10px}.home-content{padding-top:28px}.sheet{margin:auto;border-radius:24px}.bottom-nav{left:50%;transform:translateX(-50%);max-width:1040px;border:1px solid var(--line);border-bottom:0;border-radius:20px 20px 0 0}.viewer-tools button{flex:0 0 85px;font-size:10px}.viewer-head{padding-left:18px;padding-right:18px}.viewer-head h2{font-size:15px}}
@media(orientation:landscape) and (max-height:550px){.viewer-head{min-height:44px;padding-top:max(3px,env(safe-area-inset-top,0px));padding-bottom:3px}.viewer-head .icon-button{height:35px}.viewer-head small{display:none}.viewer-tools{min-height:49px;padding:3px max(10px,env(safe-area-inset-right,0px)) 3px max(10px,env(safe-area-inset-left,0px))}.viewer-tools button{flex:1;flex-direction:row;gap:7px;min-height:38px;font-size:9px}.viewer-tools button svg{width:18px;height:18px}.sheet{max-height:95dvh}.immersive .viewer-tools{min-height:40px;gap:7px}.immersive .viewer-tools button{min-width:78px}.immersive .viewer-tools #rotate{display:none}}
@media(prefers-reduced-motion:reduce){*{animation:none!important;scroll-behavior:auto!important}}

.pan-layer{position:absolute;top:0;left:0;z-index:2;touch-action:none;cursor:grab}.pan-layer:active{cursor:grabbing}.viewer-loading{z-index:3}

/* Grade choices stay readable on phones; all seven fit on wide screens. */
.grade-grid{grid-template-columns:repeat(3,minmax(0,1fr))}@media(min-width:700px){.grade-grid{grid-template-columns:repeat(4,minmax(0,1fr))}}@media(min-width:1050px){.grade-grid{grid-template-columns:repeat(7,minmax(0,1fr))}}

/* Bright observation surfaces keep the original simulation palettes readable. */
:root{color-scheme:only light;--scene-paper:#f8fbfd;--scene-ink:#193e50}
.viewer,#lab-frame{background:var(--scene-paper)}
.viewer-head{background:#ffffff;color:var(--scene-ink);border-bottom-color:#d8e5eb}
.viewer-head small{color:#4c6c7b}
.viewer-head .icon-button:hover{background:#e7f3f0}
.viewer-tools{background:#ffffff;border-top-color:#d8e5eb}
.viewer-tools button{color:#294e5e;font-size:10px;font-weight:600}
.viewer-tools button[aria-pressed=true]{background:#daf3e9;color:#086a61}
.immersive .viewer-tools{background:#fffffff7;border-color:#c5dadf;box-shadow:0 5px 22px #254c5d20}
.immersive .viewer-tools #observe{color:#086a61}
.viewer-loading{background:var(--scene-paper);color:#436676}
.spinner{border-color:#cde6e1;border-top-color:#087f7c}

/* Shared observation layout: actual CSS-sized readouts on all platforms. */
#observation-layout{display:flex;flex-direction:column;flex:1;min-height:0;min-width:0;overflow:hidden}
.lab-readouts{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:8px;padding:10px;background:#edf5f4;border-top:1px solid #d3e5e2;max-height:24dvh;overflow:auto;flex-shrink:0}
.lab-readouts>div{padding:9px 12px;border:1px solid #d6e6e2;border-radius:10px;background:white;min-width:0}
.lab-readouts small{display:block;font-size:12px;line-height:1.4;color:#587780;margin-bottom:4px}
.lab-readouts strong{display:block;font-size:17px;line-height:1.35;color:#145a61;overflow-wrap:anywhere;font-variant-numeric:tabular-nums}
.immersive .lab-readouts{display:none!important}
.lab-meta,.lab-status{font-size:11px}.lab-title{font-size:15px}.student-note{font-size:12px}.chapter-chip{font-size:13px}.setting-row small,.sheet .status-note{font-size:13px}
.viewer-tools button{font-size:11px;min-width:56px;min-height:48px}.viewer-tools{justify-content:flex-start}.viewer-tools #sim-help{min-width:48px}
@media(orientation:landscape) and (min-width:650px){#observation-layout{flex-direction:row}.lab-readouts{width:210px;grid-template-columns:1fr;max-height:none;border-top:0;border-left:1px solid #d3e5e2;align-content:start}.viewer-tools{justify-content:center}.viewer-tools button{flex:0 0 auto;padding:4px 12px}}
@media(min-width:1000px){.home-content{max-width:1220px}.lab-list{grid-template-columns:repeat(3,minmax(0,1fr))}.lab-readouts{width:240px}.viewer-head h2{font-size:17px}.viewer-tools button{font-size:12px}}
@media(orientation:portrait) and (max-width:600px){.viewer-tools{flex-wrap:wrap;justify-content:center;overflow:visible;gap:3px;padding:6px 5px calc(6px + env(safe-area-inset-bottom,0px))}.viewer-tools button{flex:0 1 calc(20% - 4px);min-width:44px;min-height:43px;font-size:10px}.immersive .viewer-tools{flex-wrap:nowrap;overflow-x:auto;justify-content:flex-start;max-width:calc(100% - 16px)}.immersive .viewer-tools button{flex:0 0 50px;min-width:50px}.immersive .viewer-tools #sim-help,.immersive .viewer-tools #sim-step,.immersive .viewer-tools #sim-example{display:none}}
.lab-description{display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden;font-size:12px;line-height:1.5;color:#6e838a;margin-top:5px;white-space:normal}.web-announcement,.web-contact{padding:18px 20px;border-radius:16px;margin:0 0 18px;border:1px solid #d5e6e0;background:#f0f8f4;color:#345f54;overflow-wrap:anywhere}.web-announcement p,.web-contact p{margin:6px 0 0;white-space:pre-line;font-size:14px;line-height:1.65}.web-contact{margin-top:24px;background:#fff}.web-contact h2{font-size:16px;margin:0}.brand #web-name{font:inherit;font-weight:750}#web-introduction{white-space:pre-line}#observation-help{white-space:pre-line}