:root{color-scheme:dark;--bg:#09121b;--panel:#101e2b;--panel2:#142534;--line:#263b4b;--text:#edf4f7;--muted:#a2b6c4;--cyan:#70e3dc;--amber:#ffc775;--violet:#b7a6fa;--red:#ff9a8e;--radius:16px;--font:Inter,"Segoe UI",Arial,sans-serif}*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;background:var(--bg);color:var(--text);font-family:var(--font);line-height:1.55;font-size:15px}button,input,select{font:inherit}button,a,input,select,summary{-webkit-tap-highlight-color:transparent}a{color:var(--cyan);text-underline-offset:4px}button{color:var(--text);border:1px solid var(--line);background:var(--panel);border-radius:8px;cursor:pointer;padding:9px 13px}button:hover{border-color:var(--cyan);background:#203747}button:focus-visible,a:focus-visible,select:focus-visible,input:focus-visible,summary:focus-visible{outline:3px solid 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@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*{animation:none!important;transition:none!important}}
@media print{.topbar,.sidebar,.step-nav,.tools{display:none}.shell{display:block}body{background:white;color:black}.panel,.fact,.metric,.formula,details{background:white;color:black;border-color:#888;break-inside:avoid}main{padding:0;max-width:none}.small,.caption,.lesson-top p,.fact .sub,.fact .label,footer{color:#444}a{color:#155}.grid{grid-template-columns:1fr 1fr}}
.media-options{display:flex;justify-content:center;gap:7px;padding:0 15px 15px;flex-wrap:wrap}.media-options:empty{display:none}.media-options button{font-size:10px;padding:5px 9px}.media-options .active{border-color:var(--cyan);color:var(--cyan);background:#1a3b41}.manufacture{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:14px;margin:20px 0}.manufacture>div{border-top:1px solid #395260;padding-top:12px}.manufacture span{display:block;color:var(--cyan);font-size:10px;letter-spacing:.1em;margin-bottom:6px}.manufacture strong{font-size:13px}.manufacture p{font-size:11px;color:var(--muted);margin:6px 0}.ct-artwork{width:100%;max-height:200px;object-fit:contain;display:block;margin:10px 0}@media(max-width:650px){.manufacture{grid-template-columns:repeat(2,minmax(0,1fr));gap:13px}.manufacture strong{font-size:12px}.media-options button{min-height:36px}}
.command-chain{display:grid;gap:10px;margin:20px 0}.command-chain>div{display:flex;gap:12px;padding:14px;border:1px solid #2f4959;background:#0d1b26;border-radius:10px}.command-chain>div.active{border-color:var(--cyan);background:#193b40}.command-chain>div>span{color:var(--cyan);font-size:11px;padding-top:3px}.command-chain strong{font-size:13px}.command-chain p{font-size:11px;color:var(--muted);margin:5px 0 0}.cooling-diagram{width:100%;display:block}.fan-rotor.is-on{transform-origin:0 0;animation:spin 1.8s linear infinite}.pump-rotor.is-on{transform-origin:0 0;animation:spin 2.8s linear infinite}.oil-flow{animation:flow 5s linear infinite}.forced-oil .oil-flow{animation-duration:2s}#directed-path{animation:flow 2.5s linear infinite}#content[data-motion="paused"] *{animation-play-state:paused!important}@keyframes spin{to{transform:rotate(360deg)}}@keyframes flow{to{stroke-dashoffset:-68}}
/* REV2: viewport-first, deliberately paged lessons. Never hide overflowed content. */
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450px);min-height:160px;object-fit:contain;margin:0 auto}.teaching-screen.single .visual-panel{width:100%}.teaching-screen .diagram-wrap svg,.teaching-screen .cooling-diagram,#preservation-graphic svg{max-height:300px;width:100%;display:block}.teaching-screen video{max-height:calc(100dvh - 430px);min-height:180px;width:100%}.teaching-screen .media-options{padding:12px 0 0;gap:8px}.teaching-screen button{min-height:42px}.teaching-screen .media-options button{font-size:12px;padding:7px 10px}.teaching-screen .source-list{display:block;font-size:14px;line-height:1.5;padding-left:18px;margin:5px 0}.teaching-screen .source-list li{margin:0 0 22px}.teaching-screen .source-link,.diagnostic-sources{font-size:12px}.diagnostic-sources{display:flex;flex-direction:column;gap:6px;margin-top:18px}.teaching-screen [data-live]{background:#17373c;border:1px solid #315b61;color:#a5fff2;border-radius:8px;padding:10px 12px;font-size:14px;font-variant-numeric:tabular-nums}.teaching-screen .command-chain{margin:10px 0;gap:8px}.teaching-screen .command-chain>div{padding:11px}.teaching-screen .command-chain strong{font-size:14px}.teaching-screen .command-chain p{font-size:12px}.teaching-screen .symptom{background:#18303f;border-left:3px solid var(--amber);padding:14px 16px;font-size:16px;line-height:1.4;margin:5px 0 18px}.report-row{border:1px dashed #749299;background:#16313c;padding:18px;font-size:18px;border-radius:9px;margin:18px 0}.step-nav{flex-shrink:0;margin:0;padding:10px 0 8px;gap:14px;min-height:63px}.step-nav button{min-height:44px;min-width:115px;font-size:13px}.step-center{display:flex;align-items:center;flex-direction:column;gap:5px;min-width:75px;max-width:230px;flex:1}.step-center span{font-size:12px;letter-spacing:.08em}.step-center progress{height:4px;width:100%;accent-color:var(--cyan);border:0}footer{flex-shrink:0;padding:6px 0;font-size:10px;line-height:1.4;min-height:28px}footer a{margin-left:auto}#overflow-note{font-size:11px;color:var(--amber);margin:4px 0 0;flex-shrink:0;line-height:1.3}.lesson-top p.sr-only{margin:0}
@media(min-width:1400px) and (min-height:850px){.teaching-screen .panel{padding:25px 30px}.teaching-screen .small,.teaching-screen .callout{font-size:15px}.teaching-screen .canvas{height:340px}.teaching-screen .canvas.tall{height:380px}.teaching-screen .visual-panel .artwork{max-height:calc(100dvh - 450px)}}
@media(max-width:1000px){.shell{grid-template-columns:180px minmax(0,1fr)}.shell main{padding:13px 16px 0}.topbar{padding:0 16px}.teaching-screen .panel{padding:17px}.teaching-screen .small,.teaching-screen .callout{font-size:14px}.screen-heading select{max-width:43%;font-size:11px}.brand{display:none}}
@media(max-width:880px){.shell{display:flex;flex-direction:column}.sidebar{overflow:visible;flex-shrink:0;padding:5px 14px;border-bottom:1px solid var(--line)}.subject{display:none}#chapters{overflow-x:auto;flex-direction:row;padding-bottom:2px;gap:5px}#chapters button{white-space:nowrap;min-height:35px;padding:6px 10px;font-size:12px}.shell main{flex:1;padding:10px 16px 0}.topbar{height:55px;min-height:55px}.lesson-top h2{font-size:19px}.lesson-tag{display:none}.screen-heading{min-height:38px;margin-bottom:7px}.screen-heading h3{font-size:14px}.screen-heading select{min-height:36px;max-width:45%;font-size:11px}.teaching-screen .canvas.tall{height:300px}.teaching-screen .panel h3{font-size:19px}}
@media(max-width:780px){.topbar{flex-wrap:nowrap;gap:7px;padding:0 12px}.topbar .back{font-size:11px;padding:5px 9px;gap:6px;white-space:nowrap}.topbar .tools{width:auto;gap:5px;margin-left:auto}.topbar .tools button{font-size:11px;padding:6px 8px;min-height:40px}.sidebar{padding:4px 12px}.shell main{padding:8px 12px 0}.lesson-top{min-height:35px;margin:0 0 5px}.lesson-top h2{font-size:18px}.lesson-top .eyebrow{font-size:8px;margin-bottom:1px}.screen-heading{display:block;min-height:0}.screen-heading h3{font-size:14px;margin:0 0 5px}.screen-heading select{width:100%;max-width:none;min-height:34px;font-size:12px;padding:5px 8px}.teaching-screen,.teaching-screen.paired{grid-template-columns:1fr;gap:12px}.teaching-screen .panel{padding:17px;border-radius:12px}.teaching-screen .panel h3{font-size:18px;margin-bottom:11px}.teaching-screen .small,.teaching-screen .callout,.teaching-screen .note-list{font-size:14px}.teaching-screen .formula .small{font-size:13px}.teaching-screen .control{margin:13px 0}.teaching-screen .control label{font-size:13px}.teaching-screen .canvas,.teaching-screen .canvas.tall{height:280px}.teaching-screen .visual-panel .artwork{max-height:calc(100dvh - 340px);min-height:150px}.teaching-screen .diagram-wrap svg,.teaching-screen .cooling-diagram,#preservation-graphic svg{max-height:235px}.teaching-screen .equation{font-size:21px}.teaching-screen .fact{padding:10px}.teaching-screen .fact .label{font-size:9px}.teaching-screen .fact .sub{font-size:10px}.teaching-screen .fact .value{font-size:23px}.teaching-screen .numbered>div{font-size:15px}.teaching-screen .source-list{font-size:14px}.teaching-screen .source-list li{margin-bottom:18px}.teaching-screen video{max-height:calc(100dvh - 350px);min-height:160px}.teaching-screen .metric b{font-size:21px}.teaching-screen .metric span{font-size:10px}.step-nav{min-height:58px;padding:7px 0;gap:7px}.step-nav button{min-width:90px;max-width:42%;font-size:11px;padding:8px 10px;line-height:1.2}.step-center{min-width:60px}.step-center span{font-size:11px}footer{min-height:25px;font-size:9px;align-items:center;gap:6px;flex-wrap:nowrap}footer strong{max-width:73%;line-height:1.25}footer a{width:auto;margin:0 0 0 auto;font-size:10px}.teaching-screen .flow>div{font-size:12px}.teaching-screen .flow b{font-size:19px}}
@media(max-height:650px) and (min-width:781px){.subject{padding-bottom:7px}.subject h1{font-size:19px}#chapters button{min-height:32px;padding:6px 7px}.sidebar{padding-top:10px}.shell main{padding-top:8px}.lesson-top{min-height:32px}.lesson-top h2{font-size:19px}.screen-heading{margin-bottom:6px;min-height:34px}.teaching-screen .panel{padding:14px}.teaching-screen .canvas,.teaching-screen .canvas.tall{height:280px}.screen-heading select{min-height:34px}.topbar{height:52px;min-height:52px}}
@media print{html,body{height:auto!important;overflow:visible!important;display:block}.topbar,.sidebar,.screen-heading,.step-nav,#overflow-note{display:none!important}.shell,main,#content{display:block!important;height:auto!important;overflow:visible!important}.teaching-screen[hidden]{display:grid!important}.teaching-screen{min-height:0;break-after:page;page-break-after:always}.panel{break-inside:avoid}footer{display:none}}

#content:focus-visible{outline:2px solid var(--cyan);outline-offset:2px}

.teaching-screen picture{display:block}
/* Rev3: sealed systems, protection functions and gas evidence. */
#sealed-architecture-graphic svg,#sealed-relay-graphic svg{display:block;width:100%;height:300px;max-height:36dvh}.gas-capabilities{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:8px;margin:12px 0}.gas-channel{border:1px solid #344e5c;border-radius:8px;padding:9px 10px;background:#0c1b27}.gas-channel b{display:block;font-size:19px}.gas-channel span{display:block;font-size:12px;color:var(--muted);line-height:1.3;margin-top:3px}.gas-channel.measured{border-color:#427a78;background:#163c40}.gas-channel.measured b{color:var(--cyan)}.gas-channel.composite{border-color:#8d7046;background:#322b20}.gas-channel.composite b{color:var(--amber)}.gas-channel.not-measured{opacity:.65}.gas-picker{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:9px;margin:16px 0}.gas-picker button{display:flex;align-items:center;gap:12px;text-align:left;min-height:52px}.gas-picker b{font-size:20px;min-width:48px;color:var(--amber)}.gas-picker span{font-size:13px}.gas-picker [aria-pressed=true]{background:#1c4b4b;border-color:var(--cyan)}#sealed-gas-evidence h4{font-size:25px;color:var(--amber)}#sealed-fit h4{font-size:16px}#sealed-model-note h4{font-size:19px}.sealed-surge{animation:sealedpulse 1.6s ease-in-out infinite}@keyframes sealedpulse{50%{opacity:.4}}@media(max-width:780px){#sealed-architecture-graphic svg,#sealed-relay-graphic svg{height:240px;max-height:31dvh}.gas-picker{gap:7px;margin:12px 0}.gas-picker button{min-height:47px;padding:8px 10px}.gas-capabilities{gap:7px}.gas-channel{padding:8px}.gas-channel b{font-size:18px}.gas-channel span{font-size:12px}}