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/* Progressive, multi-open topic lessons */
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.lesson-section-footer{margin-top:20px;padding-top:14px;border-top:1px solid var(--line)}.lesson-section-footer a{display:inline-block;color:var(--teal);font-size:11px;font-weight:700;text-decoration:none}.lesson-section-footer a:hover{text-decoration:underline}
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.accordion-state svg{width:18px;height:18px;display:block;fill:none;stroke:currentColor;stroke-width:2.25;stroke-linecap:round;stroke-linejoin:round}
.sec-practice-group{margin-top:10px}.sec-practice-group .lesson-cards{max-width:calc(50% - 5px)}@media(max-width:700px){.sec-practice-group .lesson-cards{max-width:none}}
.lesson-accordion-panel{min-width:0}.lesson-accordion-panel .reading-grid{width:100%;min-width:0;grid-template-columns:minmax(0,1fr)}.lesson-accordion-panel .reading-main{width:100%;min-width:0}.lesson-accordion-panel .reading-main>*{min-width:0;max-width:100%}@media(max-width:560px){.lesson-accordion-panel .physics-diagram{overflow-x:auto;overflow-y:hidden}}

/* Shared visual language for multi-stage teaching diagrams. */
.teaching-svg{font-family:Inter,Arial,sans-serif;color:#17313a}.teaching-svg .panel>rect,.teaching-svg .process>rect,.teaching-svg .comparison>rect{fill:#fbfcfb;stroke:#cbd8d4;stroke-width:1.5}.teaching-svg .panel-title{fill:#12343f;font-size:16px;font-weight:800;letter-spacing:.035em}.teaching-svg .label{fill:#17313a;font-size:18px;font-weight:750}.teaching-svg .small{fill:#53696e;font-size:13px}.teaching-svg .note{fill:#65787c;font-size:12px}.teaching-svg .formula{fill:#12343f;font:700 17px Georgia,serif}.teaching-svg .wire,.teaching-svg .thin,.teaching-svg .axis,.teaching-svg .lens,.teaching-svg .coil{fill:none;stroke:#405b61;stroke-width:3}.teaching-svg .thin{stroke-width:2}.teaching-svg .axis{stroke:#899a9d;stroke-width:2}.teaching-svg .lens{stroke:#49769d;stroke-width:5}.teaching-svg .current,.teaching-svg .motion,.teaching-svg .force,.teaching-svg .flow,.teaching-svg .field,.teaching-svg .rotation,.teaching-svg .flux{fill:none;stroke-width:4}.teaching-svg .current,.teaching-svg .flow{stroke:#167a72}.teaching-svg .motion,.teaching-svg .rotation{stroke:#c98724}.teaching-svg .force{stroke:#a9574a}.teaching-svg .field,.teaching-svg .flux{stroke:#49769d}.teaching-svg .ib{stroke:#167a72}.teaching-svg .ic{stroke:#a9574a}.teaching-svg .ie{stroke:#49769d}.teaching-svg .ib-text{fill:#167a72}.teaching-svg .ic-text{fill:#a9574a}.teaching-svg .nfill{fill:#dfeff7;stroke:#49769d}.teaching-svg .pfill{fill:#fff0ec;stroke:#a9574a}.teaching-svg .lamp{fill:#fff5df;stroke:#c98724;stroke-width:3}.teaching-svg .device{fill:#e6f1ee;stroke:#167a72;stroke-width:3}.teaching-svg .resistor{fill:#edf3f8;stroke:#49769d}.teaching-svg .magnet,.teaching-svg .meter,.teaching-svg .ring{fill:#edf3f8;stroke:#405b61;stroke-width:2}.teaching-svg .needle{stroke:#a9574a;stroke-width:4}.teaching-svg .north{fill:#a9574a}.teaching-svg .south{fill:#49769d}.teaching-svg .focus{fill:#12343f;font-size:13px}.teaching-svg .object{stroke:#17313a;stroke-width:5}.teaching-svg .image{stroke:#a9574a;stroke-width:5}.teaching-svg .ray{fill:none;stroke-width:4}.teaching-svg .ray.one{stroke:#c98724}.teaching-svg .ray.two{stroke:#167a72}.teaching-svg .extension{fill:none;stroke:#899a9d;stroke-width:2;stroke-dasharray:7 6}.teaching-svg .steps{fill:#425b61;font-size:14px}.teaching-svg .process>g>circle{fill:#167a72;stroke:none}.teaching-svg .process>g>circle+text{fill:white;font-size:14px;font-weight:800;text-anchor:middle}.teaching-svg .process>g>text:not(:first-of-type){fill:#425b61;font-size:13px}.teaching-svg .comparison{fill:#17313a;font-size:15px;font-weight:650}.physics-diagram .teaching-svg text{paint-order:stroke;stroke:#fff;stroke-width:0}.physics-diagram figcaption{font-size:11px}
@media(max-width:560px){.physics-diagram{overflow-x:auto}.physics-diagram .teaching-svg{min-width:700px}.physics-diagram figcaption{position:sticky;left:0;max-width:calc(100vw - 30px);background:#fff}}
.diagram-attribution{display:block;margin-top:6px;color:#748488;font-size:9px;line-height:1.45}.diagram-attribution a{color:var(--teal);text-decoration:underline;text-underline-offset:2px}

.reading-grid-solo{grid-template-columns:minmax(0,820px);justify-content:start}
.video-resources{overflow:hidden;border:1px solid #c9d9d5;border-radius:13px;background:#fff}
.video-resources>header{display:flex;align-items:center;gap:13px;padding:17px 20px;border-bottom:1px solid var(--line);background:var(--teal-pale)}
.video-resources>header>span{width:34px;height:34px;display:grid;place-items:center;border-radius:50%;background:var(--teal);color:#fff;font-size:13px}
.video-resources .eyebrow{margin-bottom:3px}
.video-resources h2{margin:0;color:var(--navy);font:600 20px/1.25 Georgia}
.video-list{display:grid}
.video-list a{display:grid;grid-template-columns:1fr auto;align-items:center;gap:20px;padding:18px 20px;border-bottom:1px solid var(--line);color:inherit;text-decoration:none}
.video-list a:hover{background:#f8faf8}
.video-list b,.video-list span{display:block}
.video-list b{color:var(--navy);font:600 16px Georgia}
.video-list span{margin-top:4px;color:var(--teal);font-size:9px;font-weight:800;letter-spacing:.08em;text-transform:uppercase}
.video-list p{margin:8px 0 0;color:#586d71;font-size:12px;line-height:1.55}
.video-list em{color:var(--teal);font-size:10px;font-style:normal;font-weight:750;white-space:nowrap}
.video-resources>small{display:block;padding:10px 20px;color:#7a898c;font-size:9px;line-height:1.45}
@media(max-width:560px){.video-list a{grid-template-columns:1fr}.video-list em{white-space:normal}}

/* Topic-page design system refinements */
.topbar{grid-template-columns:42px 196px minmax(120px,1fr) auto;gap:10px;padding:0 18px}
#menu-button{display:grid;place-items:center;width:36px;padding:0;font-size:16px}
.sidebar{width:238px}.workspace{margin-left:238px;transition:margin-left .2s ease}.side-head{display:flex;align-items:flex-start;justify-content:space-between;padding:20px 14px 14px 20px}.side-head h2{margin-bottom:0;font-size:21px}.side-collapse{width:28px;height:28px;border:1px solid var(--line);border-radius:8px;background:#fff;color:var(--muted);font-size:19px;cursor:pointer}.nav-collapsed .sidebar{transform:translateX(-100%)}.nav-collapsed .workspace{margin-left:0}.nav-collapsed .side-collapse{transform:rotate(180deg)}
.mode-switch{display:flex;padding:3px;border:1px solid var(--line);border-radius:10px;background:#f1f4f2}.mode-switch button{min-height:29px;padding:0 10px;border:0;border-radius:7px;background:transparent;color:#65787c;font-size:10px;font-weight:750;cursor:pointer}.mode-switch button.active{background:#fff;color:var(--teal);box-shadow:0 1px 3px #17313a18}.teacher-action{border-color:#9ebdb8;color:var(--teal)}
.view{padding-top:44px}.topic-hero{min-height:300px;padding:42px 46px}.topic-hero h1{font-size:clamp(44px,5.7vw,64px)}.topic-hero>div>p:not(.eyebrow){font-size:18px}.overview-head{margin-top:48px}.overview-head h2{font-size:34px}.lesson-title{margin-bottom:36px}.lesson-title h1{font-size:clamp(38px,5vw,54px)}.lesson-summary{font-size:18px}
.lesson-cards{gap:0 28px}.lesson-card{min-height:92px;padding:16px 4px;border:0;border-bottom:1px solid var(--line);border-radius:0;background:transparent}.lesson-card:hover{border-color:#9ebdb8;background:#ffffff80;box-shadow:none;transform:none}.lesson-card b{font-size:17px}
.student-notes{padding:8px 0 24px;border:0;border-bottom:1px solid var(--line);border-radius:0;background:transparent}.student-notes ul{font-size:14px}.plain-explanation{padding:4px 0 18px}.plain-explanation>p:not(.eyebrow){margin:0 0 14px;color:#4d6267;font-size:14px;line-height:1.72}.plain-explanation>p:not(.eyebrow):last-child{margin-bottom:0}
.physics-diagram{margin:8px 0 22px;overflow:visible;border:0;border-radius:0;background:transparent}.diagram-head{padding:10px 0;border:0;background:transparent}.diagram-head b{font-size:12px}.physics-diagram svg{width:100%;max-height:500px;padding:18px 3%;background:#fff;border-radius:10px}.physics-diagram figcaption{padding:10px 4px;border:0;color:#687b7f}
.equation .formula{max-width:100%;padding:23px 8px;overflow-wrap:anywhere;font-size:clamp(20px,3.5vw,30px);white-space:normal}.equation .formula>span{display:inline-block;max-width:100%;padding:0 4px}
.reading-grid{grid-template-columns:minmax(0,780px) 170px;gap:38px}.complete,.progress-line,.side-head small,.side-foot,.template-note{display:none!important}
.classroom-display .view{max-width:1320px}.classroom-display .reading-grid{grid-template-columns:minmax(0,940px) 180px}.classroom-display .lesson-title h1{font-size:clamp(46px,5.4vw,62px)}.classroom-display .lesson-summary{font-size:22px}.classroom-display .student-notes ul,.classroom-display .plain-explanation>p:not(.eyebrow),.classroom-display .teaching-block p{font-size:16px}.classroom-display .physics-diagram svg{max-height:610px}.classroom-display .reveal{font-size:12px;padding:11px 15px}.classroom-action.active{border-color:#9ebdb8;background:var(--teal-pale);color:var(--teal)}

@media(max-width:1100px){.reading-grid,.classroom-display .reading-grid{grid-template-columns:minmax(0,1fr)}.lesson-tools{display:none}}
@media(max-width:900px){.topbar{grid-template-columns:38px 1fr auto;padding:0 12px}.brand{min-width:0}.breadcrumb{display:none}.sidebar,.nav-collapsed .sidebar{width:min(88vw,340px);transform:translateX(-105%);transition:transform .2s}.nav-open .sidebar{transform:none;box-shadow:20px 0 45px #17313a25}.nav-open .scrim{display:block;position:fixed;inset:68px 0 0;z-index:15;border:0;background:#17313a55}.workspace,.nav-collapsed .workspace{margin-left:0}.side-collapse{display:none}.mode-switch button{padding-inline:8px}.teacher-action{position:fixed;right:12px;bottom:14px;z-index:14;box-shadow:0 6px 20px #17313a25}.view{padding:32px clamp(20px,4vw,34px) 70px}.topic-hero{padding:34px 30px}.topic-hero h1{font-size:50px}.lesson-title h1{font-size:44px}.teacher .lesson-title h1{font-size:48px}}
@media(max-width:560px){.topbar{height:62px}.sidebar{inset-top:62px}.brand small{display:none}.brand-mark{width:33px;height:33px}.mode-switch button{min-height:28px;padding-inline:7px}.workspace{padding-top:62px}.view{padding:27px 15px 60px}.topic-hero{padding:28px 22px;border-radius:15px}.topic-hero h1{font-size:42px}.topic-hero>div>p:not(.eyebrow){font-size:16px}.lesson-title h1{font-size:38px}.teacher .lesson-title h1{font-size:42px}.lesson-summary{font-size:17px}.lesson-cards{grid-template-columns:1fr}.physics-diagram svg{padding:12px 0;border-radius:8px}.equation .formula{font-size:22px}.teaching-block>p,.teaching-block>h3,.teaching-block>.formula,.teaching-block>.prompt,.teaching-block>ol,.teaching-block>button,.teaching-block>.reveal-panel,.teaching-block>.input-row,.teaching-block>output,.teaching-block>.identify,.teaching-block>.half-control,.teaching-block>.sim,.teaching-block>.mixed{margin-left:16px;margin-right:16px}.input-row label{width:calc(33% - 6px)}.input-row input{width:100%}.input-row button{width:100%}.half-control,.sim{grid-template-columns:1fr}#sim-atoms{grid-template-columns:repeat(8,1fr)}}

/* Approved template density and multipart solution treatment */
.teaching-block>header{padding:9px 15px}.teaching-block h3{margin-top:15px;margin-bottom:4px}.teaching-block p{margin-top:7px;margin-bottom:16px}.definition h3{font-size:21px}.definition>p{margin-bottom:16px}.equation .formula{padding-top:19px;padding-bottom:19px}.reveal{margin-bottom:16px!important}.reveal-panel{margin-bottom:17px!important;padding:13px 16px}.solution-parts{display:grid;gap:0}.solution-parts section{padding:12px 0;border-bottom:1px solid var(--line)}.solution-parts section:first-child{padding-top:2px}.solution-parts section:last-child{padding-bottom:2px;border-bottom:0}.solution-parts b{display:block;color:var(--navy);font-size:11px;letter-spacing:.03em}.solution-parts p{margin:5px 0 0!important;color:#4d6267;font-size:12px;line-height:1.6}

/* Course-wide navigation */
.nav-tabs{display:grid;grid-template-columns:1fr 1fr;gap:4px;margin:0 12px 12px;padding:3px;border:1px solid #d4ddd9;border-radius:9px;background:#e4e9e5}.nav-tabs button{min-height:29px;padding:0 6px;border:0;border-radius:6px;background:transparent;color:#6a7b7e;font-size:9px;font-weight:750;cursor:pointer}.nav-tabs button.active{background:#fff;color:var(--teal);box-shadow:0 1px 3px #17313a12}.nav-tabs button:disabled{cursor:not-allowed;opacity:.42}
#course-nav,#lesson-nav{flex:1;overflow:auto;padding:0 12px 20px}#course-nav>p,#lesson-nav>p{margin:18px 10px 6px;color:#82908f;font-size:9px;font-weight:800;letter-spacing:.11em;text-transform:uppercase}#course-nav a,#lesson-nav a{min-height:35px;display:grid;grid-template-columns:25px minmax(0,1fr) auto;align-items:center;gap:7px;padding:6px 9px;border-radius:8px;color:#53686c;font-size:11px;text-decoration:none}#course-nav a:hover,#course-nav a.current,#lesson-nav a:hover,#lesson-nav a.current{background:white;color:var(--teal);box-shadow:0 1px 0 #17313a08}#course-nav a span,#lesson-nav a span{font-family:ui-monospace,monospace;font-size:9px}#course-nav a b,#lesson-nav a b{min-width:0;font-weight:620}#course-nav a em{padding:2px 5px;border-radius:5px;background:var(--teal-pale);color:var(--teal);font-size:7px;font-style:normal;font-weight:800;text-transform:uppercase}.side-head h2{max-width:175px;line-height:1.05}
@media(max-width:900px){.sidebar,.nav-collapsed .sidebar{inset:68px auto 0 0;width:min(88vw,300px);max-width:calc(100vw - 12px);overflow:hidden;box-sizing:border-box}.side-head{padding:17px 12px 11px 16px}.side-head h2{max-width:none;font-size:20px}.nav-tabs{margin:0 8px 8px}#course-nav,#lesson-nav{min-width:0;min-height:0;padding:0 7px max(16px,env(safe-area-inset-bottom));overflow-x:hidden;overflow-y:auto;overscroll-behavior:contain;scrollbar-width:none;touch-action:pan-y}#course-nav::-webkit-scrollbar,#lesson-nav::-webkit-scrollbar{display:none}#course-nav>p,#lesson-nav>p{margin:14px 8px 4px}#course-nav a,#lesson-nav a{grid-template-columns:22px minmax(0,1fr) auto;gap:5px;padding:6px 7px}#course-nav a b,#lesson-nav a b{white-space:normal;overflow-wrap:break-word;line-height:1.3}}
@media(max-width:560px){.sidebar,.nav-collapsed .sidebar{inset:62px auto 0 0;width:min(91vw,292px);max-width:calc(100vw - 8px)}.nav-open .scrim{inset:62px 0 0}.side-head{padding-top:14px;padding-bottom:9px}#course-nav a,#lesson-nav a{grid-template-columns:20px minmax(0,1fr) auto;gap:4px;padding-inline:6px}}
.course-heading{max-width:780px;margin-bottom:50px}.course-heading h1{margin:0;color:var(--navy);font:600 clamp(48px,6vw,66px)/1 Georgia;letter-spacing:-.04em}.course-heading>p:last-child{max-width:650px;margin:18px 0 0;color:#52676c;font:19px/1.55 Georgia}.course-group{margin:34px 0}.course-group>h2{margin:0 0 10px;color:#68797d;font-size:10px;letter-spacing:.12em;text-transform:uppercase}.course-topic-grid{display:grid;grid-template-columns:1fr 1fr;gap:0 28px}.course-topic-card{min-height:76px;display:grid;grid-template-columns:34px minmax(0,1fr) auto;align-items:center;gap:10px;padding:13px 4px;border-bottom:1px solid var(--line);color:inherit;text-decoration:none}.course-topic-card:hover{background:#ffffff90}.course-topic-card>span{color:var(--teal);font:700 10px ui-monospace,monospace}.course-topic-card b,.course-topic-card small{display:block}.course-topic-card b{color:var(--navy);font:600 17px Georgia}.course-topic-card small{margin-top:4px;color:#7a8a8d;font-size:9px}.course-topic-card em{color:var(--teal);font-size:9px;font-style:normal;font-weight:800}.course-topic-card.ready{border-color:#b9d1cb}
.course-practice-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px;margin:-18px 0 30px}.course-practice-card{display:grid;grid-template-columns:auto minmax(0,1fr);align-items:center;gap:13px;padding:15px 17px;border:1px solid #9fc8c0;border-radius:14px;background:linear-gradient(135deg,#eaf5f1,#fff);color:inherit;text-decoration:none}.course-practice-card>span{width:40px;height:40px;display:grid;place-items:center;border-radius:50%;background:var(--teal);color:#fff;font-size:21px}.course-practice-card .eyebrow{margin:0 0 2px}.course-practice-card h2{margin:0;color:var(--navy);font:600 21px Georgia}.course-practice-card p:last-child{margin:4px 0 0;color:#52676c;font-size:14px;line-height:1.4}.course-practice-card>b{grid-column:2;color:var(--teal);font-size:14px}.course-practice-card:hover,.course-practice-card:focus-visible{border-color:var(--teal);box-shadow:0 6px 20px #17313a10}.course-nav .nav-practice,.nav-practice{margin:4px 8px 10px;border:1px solid #9fc8c0;border-radius:8px;background:#eaf5f1}
.seo-route-boot .seo-topic-page>.course-practice-grid,.seo-route-boot .seo-topic-page>.seo-lessons,.seo-route-boot .seo-activity-page>p{display:none}
@media(max-width:760px){.course-topic-grid,.course-practice-grid{grid-template-columns:1fr}.course-heading{margin-bottom:38px}.course-practice-grid{margin-top:-12px}.course-practice-card{padding:16px}}
@media(max-width:480px){.course-heading h1{font-size:46px}.course-heading>p:last-child{font-size:17px}.course-topic-card{grid-template-columns:28px minmax(0,1fr) auto}}
.route-status{max-width:720px;margin:80px auto;padding:40px;border:1px solid var(--line);border-radius:13px;background:#fff;box-shadow:var(--shadow)}.route-status h1{margin:8px 0 12px;color:var(--navy);font:600 36px Georgia}.route-status>p:not(.eyebrow){color:var(--muted);line-height:1.6}.route-status .primary{display:inline-flex;margin-top:14px;padding:11px 17px;border:0;border-radius:9px;background:var(--teal);color:#fff;font-weight:700;cursor:pointer}

/* Responsive tables and mathematical notation */
.data-table-wrap{margin:4px 0 20px}.data-table-wrap>.eyebrow{margin-bottom:10px}.table-scroll{max-width:100%;overflow-x:auto;border:1px solid var(--line);border-radius:10px;background:#fff;-webkit-overflow-scrolling:touch}.data-table-wrap table{width:100%;min-width:430px;border-collapse:collapse;color:#40565b;font-size:12px}.data-table-wrap th,.data-table-wrap td{padding:11px 14px;border-bottom:1px solid var(--line);text-align:left}.data-table-wrap th{background:#f1f6f3;color:var(--navy);font-size:10px;letter-spacing:.04em}.data-table-wrap tr:last-child td{border-bottom:0}.fraction{display:inline-grid;grid-template-rows:auto auto;max-width:100%;vertical-align:middle;margin:0 .18em;line-height:1.05;text-align:center}.fraction>span{display:block;min-width:1.1em;padding:.12em .3em;overflow-wrap:anywhere}.fraction>span:first-child{border-bottom:1.5px solid currentColor}.equation .formula{max-width:100%;overflow-wrap:anywhere}.equation .formula br{display:block;content:"";margin-top:.55em}.equation-line{display:flex!important;align-items:center;justify-content:center;gap:.18em;max-width:100%;flex-wrap:wrap}.equation-line+.equation-line{margin-top:.8em;padding-top:.7em!important;border-top:1px solid #d9e2ed}.equation-name{flex:0 0 100%;color:#526a7f;font:700 .42em/1.25 system-ui,sans-serif;letter-spacing:.03em;text-transform:uppercase}
.radical{display:inline-flex;align-items:flex-start;vertical-align:middle;margin-left:.12em}.radical>span:first-child{font-size:1.45em;line-height:.9}.radicand{display:inline-flex;align-items:center;padding:.05em .12em 0;border-top:1.5px solid currentColor}.bracketed-fraction{display:inline-flex;align-items:center;gap:.08em}
.practical-result{display:flex;align-items:center;justify-content:center;gap:.85rem;flex-wrap:wrap;padding:.9rem 1rem;border-top:1px solid #d6e2df;background:#f5f9f8;color:#17313a}.practical-result>span{font-size:.72rem;font-weight:800;letter-spacing:.08em;text-transform:uppercase;color:#53696e}.practical-result .formula{font:700 clamp(1.2rem,3vw,1.65rem)/1.25 Georgia,serif}.preferred-diagram img,.handover-diagram img,.full-teaching-card img,.source-diagrams img,.physics-diagram img{display:block;width:100%;max-width:100%;height:auto;object-fit:contain}.preferred-diagram figure,.handover-diagram,.full-teaching-card,.source-diagrams figure,.physics-diagram{min-width:0;max-width:100%;overflow:hidden}
@media(max-width:560px){.data-table-wrap table{font-size:11px}.data-table-wrap th,.data-table-wrap td{padding:10px 12px}.equation .formula{white-space:normal}.equation .formula>span{min-width:0}.fraction{font-size:.88em}}

/* Approved teacher-source content */
.source-prose,.source-list{padding:2px 0}.source-prose p{margin:0;color:#4d6267;font-size:14px;line-height:1.72}.source-list ul{display:grid;gap:9px;margin:0;padding-left:21px;color:#40565b;font-size:14px;line-height:1.62}.source-list li::marker{color:var(--teal)}.source-subheading{padding-top:9px;border-bottom:1px solid var(--line)}.source-subheading h2{margin:0 0 10px;color:var(--navy);font:600 26px/1.2 Georgia}.source-diagrams{margin:5px 0 20px}.source-diagram-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px}.source-diagram-grid figure{margin:0;overflow:hidden;border:1px solid var(--line);border-radius:11px;background:#fff}.source-diagram-grid img{display:block;width:100%;height:auto;max-height:440px;object-fit:contain;padding:14px}.source-diagram-grid figcaption{padding:9px 12px;border-top:1px solid var(--line);color:#748488;font-size:9px}.teacher .source-prose p,.teacher .source-list ul{font-size:16px}.teacher .source-subheading h2{font-size:31px}
.preferred-diagram{margin:8px 0 24px}.preferred-diagram>p{margin:0 0 9px}.preferred-diagram figure{margin:0;overflow:hidden;border:1px solid var(--line);border-radius:13px;background:#fff;box-shadow:0 5px 18px #17313a0b}.preferred-diagram a{display:block;background:#fff}.preferred-diagram img{display:block;width:100%;height:auto;object-fit:contain}.preferred-diagram figcaption{display:flex;align-items:center;justify-content:space-between;gap:18px;padding:11px 14px;border-top:1px solid var(--line);color:#53696e;font-size:12px;line-height:1.45}.preferred-diagram figcaption span{font-weight:700}.preferred-diagram figcaption small{color:#748488;text-align:right}
.preferred-diagram--medium{max-width:760px;margin-left:auto;margin-right:auto}.preferred-diagram--narrow{max-width:620px;margin-left:auto;margin-right:auto}
@media(max-width:620px){.source-diagram-grid{grid-template-columns:1fr}.source-diagram-grid img{padding:8px}.source-subheading h2{font-size:23px}.preferred-diagram{margin-bottom:18px}.preferred-diagram figcaption{align-items:flex-start;flex-direction:column;gap:3px;padding:9px 10px}.preferred-diagram figcaption small{text-align:left}}
.equation .formula .equation-line{flex-wrap:nowrap}
.handover-diagrams,.full-teaching-diagrams{margin:8px 0 24px}.handover-diagrams>p,.full-teaching-diagrams>p{margin:0 0 9px}.handover-diagram-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px}.handover-diagram{display:flex;flex-direction:column;margin:0;overflow:hidden;border:1px solid var(--line);border-radius:12px;background:#fff;box-shadow:0 5px 18px #17313a0b}.handover-diagram img{display:block;width:100%;height:auto;aspect-ratio:auto;object-fit:contain;background:#fff}.handover-diagram--level1{align-self:start}.handover-diagram figcaption{display:flex;align-items:center;justify-content:space-between;gap:12px;padding:9px 12px;border-top:1px solid var(--line);color:#53696e;font-size:11px;line-height:1.4}.handover-diagram figcaption span{color:#748488;font-size:10px;white-space:nowrap}.full-teaching-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px}.full-teaching-card{display:grid;margin:0;overflow:hidden;border:1px solid var(--line);border-radius:12px;background:#fff;box-shadow:0 5px 18px #17313a0b}.full-teaching-card img{display:block;width:100%;height:auto;max-height:310px;object-fit:contain;background:#fff}.full-teaching-card>div{display:flex;align-items:center;justify-content:space-between;gap:12px;padding:10px 12px;border-top:1px solid var(--line)}.full-teaching-card b{color:#435b60;font-size:12px;line-height:1.35}.open-full-diagram{flex:0 0 auto;padding:7px 10px;border:1px solid #9dbbb6;border-radius:7px;background:#fff;color:var(--teal);font:700 10px/1.2 inherit;cursor:pointer}.open-full-diagram:hover,.open-full-diagram:focus-visible{border-color:var(--teal);background:var(--teal-pale)}#diagram-viewer{width:min(96vw,1500px);max-width:none;height:min(94vh,1100px);max-height:none;padding:0;border:0;border-radius:14px;background:#fff;box-shadow:0 25px 80px #0c252f66}#diagram-viewer::backdrop{background:#102d36c4;backdrop-filter:blur(3px)}.diagram-viewer-shell{display:grid;grid-template-rows:auto minmax(0,1fr);height:100%}.diagram-viewer-shell header{display:flex;align-items:center;justify-content:space-between;gap:20px;padding:12px 16px;border-bottom:1px solid var(--line)}.diagram-viewer-shell h2{margin:0;color:var(--navy);font:600 20px/1.25 Georgia}.diagram-viewer-shell button{width:38px;height:38px;border:0;border-radius:50%;background:#eef5f3;color:#496268;font-size:25px;line-height:1;cursor:pointer}.diagram-viewer-canvas{min-height:0;overflow:auto;padding:14px;background:#f5f8f7}.diagram-viewer-canvas img{display:block;width:auto;max-width:100%;height:auto;max-height:none;margin:auto;background:#fff}@media(max-width:700px){.handover-diagram-grid,.full-teaching-grid{grid-template-columns:1fr}.handover-diagram figcaption{align-items:flex-start;flex-direction:column;gap:2px}.full-teaching-card>div{align-items:flex-start;flex-direction:column}.full-teaching-card img{max-height:none}#diagram-viewer{width:100vw;height:100dvh;border-radius:0}.diagram-viewer-shell header{padding:10px 12px}.diagram-viewer-shell h2{font-size:17px}.diagram-viewer-canvas{padding:8px}}

.video-marker{width:19px;height:19px;display:grid;place-items:center!important;border-radius:50%;background:var(--teal-pale);color:var(--teal)!important;font-size:7px!important}
.mastery-panel{margin:42px 0;padding:24px;border:1px solid #bfd4ce;border-radius:14px;background:#f8fbf9}
.mastery-panel>header{display:flex;align-items:center;justify-content:space-between;gap:20px;margin-bottom:18px}
.mastery-panel h2{margin:0;color:var(--navy);font:600 27px Georgia}
.mastery-panel>header strong{min-width:62px;padding:11px;border-radius:10px;background:var(--teal);color:#fff;font:600 19px Georgia;text-align:center}
.mastery-list{display:grid;grid-template-columns:1fr 1fr;gap:8px 20px}
.mastery-list label{display:flex;align-items:flex-start;gap:9px;padding:9px 0;color:#4d6267;font-size:12px;line-height:1.45;cursor:pointer}
.mastery-list input{width:17px;height:17px;margin:0;accent-color:var(--teal)}
.mastery-panel>small{display:block;margin-top:14px;color:#7a898c;font-size:9px}
.attempt-gate{display:grid;gap:8px;margin:12px 22px 12px;padding:14px;border-radius:9px;background:#f5f7f5}
.attempt-gate label{display:grid;gap:7px;color:#53696d;font-size:10px;font-weight:750}
.attempt-gate textarea,.short-test textarea{width:100%;resize:vertical;padding:10px;border:1px solid #bdcbc7;border-radius:7px;background:#fff;color:var(--ink);font:12px/1.5 inherit}
.short-test textarea.answer-missing{border-color:var(--red);background:var(--red-pale);box-shadow:0 0 0 2px #a9574a18}
.attempt-gate button,.finish-test{justify-self:start;padding:9px 13px;border:0;border-radius:7px;background:var(--teal);color:#fff;font-size:10px;font-weight:750;cursor:pointer}
.attempt-gate button:disabled,.finish-test:disabled,.reveal:disabled{cursor:not-allowed;opacity:.45}
.attempt-gate small{color:#7b8a8c;font-size:9px}.attempt-gate.submitted{border:1px solid #b7d4cc;background:var(--teal-pale)}.attempt-gate.submitted .attempt-feedback{color:var(--teal);font-weight:700}
.paper-attempt-reminder{display:grid;gap:3px;margin:14px 18px 10px;padding:11px 13px;border-left:3px solid var(--teal);background:#f5f8f6;color:#526a70}.paper-attempt-reminder strong{color:var(--navy);font-size:13px}.paper-attempt-reminder span{font-size:12px;line-height:1.45}
.teacher .attempt-gate{display:none}.teacher .short-test .test-solution{display:block}.teacher .short-test textarea{display:none}
.short-test{overflow:hidden;border:1px solid #b9d0ca;border-radius:13px;background:#fff}
.short-test>header{display:flex;align-items:center;justify-content:space-between;gap:20px;padding:20px 22px;background:var(--teal-pale)}
.short-test h2{margin:0;color:var(--navy);font:600 24px Georgia}.short-test>header strong{color:var(--teal);font-size:10px}
.test-questions{display:grid;gap:0}.test-questions article{padding:18px 22px;border-bottom:1px solid var(--line)}
.test-questions h3{margin:0 0 11px;color:var(--navy);font:600 16px/1.45 Georgia}
.test-solution{display:none;margin-top:12px;padding:13px;border-radius:8px;background:#f4f7f5;color:#4d6267;font-size:12px;line-height:1.55}.short-test.marked .test-solution{display:block}
.finish-test{margin:18px 22px}.short-test>output{display:block;margin:0 22px 18px;color:var(--teal);font-size:11px}
#teacher-lock{width:min(430px,calc(100vw - 30px));padding:0;border:0;border-radius:15px;box-shadow:0 25px 80px #0c252f55;color:var(--ink)}
#teacher-lock::backdrop{background:#102d36a8;backdrop-filter:blur(3px)}#teacher-lock form{position:relative;display:grid;gap:13px;padding:28px}
#teacher-lock h2{margin:0;color:var(--navy);font:600 29px Georgia}#teacher-lock p:not(.eyebrow){margin:0;color:#607377;font-size:12px;line-height:1.6}
#teacher-lock label{display:grid;gap:6px;color:#52696d;font-size:10px;font-weight:800;text-transform:uppercase}#teacher-lock input{padding:11px;border:1px solid #b8c9c5;border-radius:8px;font-size:14px}
#teacher-lock .primary{justify-self:start;padding:10px 14px;border:0;border-radius:8px;background:var(--teal);color:#fff;font-size:11px;font-weight:800;cursor:pointer}.dialog-close{position:absolute;right:16px;top:14px;border:0;background:none;color:#718286;font-size:23px;cursor:pointer}#teacher-code-feedback{min-height:15px;color:var(--red);font-size:10px}
@media(max-width:700px){.mastery-list{grid-template-columns:1fr}.mastery-panel{padding:19px}.mastery-panel h2{font-size:23px}.short-test>header{align-items:flex-start;flex-direction:column}.attempt-gate{margin-inline:16px}.paper-attempt-reminder{margin-inline:14px}}

/* Official SEC sample-question library */
.sec-topic-links{margin:34px 0;padding:22px;border:1px solid #b9d1cb;border-radius:14px;background:#f8fbf9}.sec-topic-links header{display:flex;align-items:end;justify-content:space-between;gap:18px}.sec-topic-links h2{margin:0;color:var(--navy);font:600 27px Georgia}.sec-topic-links header>a{color:var(--teal);font-size:10px;font-weight:800;text-decoration:none}.sec-topic-links>p{color:#607377;font-size:12px;line-height:1.55}.sec-topic-links>div{display:grid;grid-template-columns:1fr 1fr;gap:8px 18px}.sec-topic-links>div>a{display:grid;gap:4px;padding:11px 0;border-top:1px solid var(--line);color:inherit;text-decoration:none}.sec-topic-links>div b{color:var(--navy);font:600 13px Georgia}.sec-topic-links>div span{color:#66797d;font-size:10px}
.sec-question-link{display:grid;gap:5px;margin:8px 0 18px;padding:16px 18px;border:1px solid #b9d1cb;border-radius:11px;background:#f8fbf9;color:inherit;text-decoration:none}.sec-question-link span{color:var(--teal);font-size:8px;font-weight:800;letter-spacing:.08em;text-transform:uppercase}.sec-question-link b{color:var(--navy);font:600 17px Georgia}.sec-question-link p{margin:0;color:#607377;font-size:11px}.sec-question-link em{color:var(--teal);font-size:9px;font-style:normal;font-weight:800}
.sec-question-shell{display:grid;gap:18px}.sec-source-banner{display:flex;align-items:flex-start;justify-content:space-between;gap:24px;padding:22px;border:1px solid #9fc4ba;border-radius:13px;background:linear-gradient(135deg,#edf7f3,#fff)}.sec-source-banner h2{margin:0;color:var(--navy);font:600 28px/1.2 Georgia}.sec-source-banner p:last-child{margin:8px 0 0;color:#597075}.sec-source-banner>span{padding:7px 9px;border-radius:7px;background:var(--teal);color:#fff;font-size:8px;font-weight:800;letter-spacing:.08em;text-transform:uppercase;white-space:nowrap}.sec-related{display:flex;align-items:center;gap:9px;flex-wrap:wrap}.sec-related b{color:#7b8a8c;font-size:9px;text-transform:uppercase}.sec-related a{padding:6px 9px;border:1px solid #bdd1cc;border-radius:999px;color:var(--teal);font-size:9px;font-weight:750;text-decoration:none}.sec-disclaimer{padding:15px 17px;border:1px solid #d9c785;border-radius:10px;background:#fffaf0;color:#665a32}.sec-disclaimer strong{display:block;margin-bottom:5px;color:#574a22;font-size:10px;letter-spacing:.06em;text-transform:uppercase}.sec-disclaimer p{margin:0;font-size:12px;line-height:1.55}.sec-preservation-note{margin:0;padding:12px 14px;border-left:3px solid var(--teal);background:#f5f8f6;color:#5e7276;font-size:11px;line-height:1.55}.sec-page-stack{display:grid;gap:14px}.sec-page-stack figure{margin:0;overflow:hidden;border:1px solid #c9d3d0;border-radius:10px;background:#fff;box-shadow:0 4px 14px #17313a0a}.sec-page-stack img{display:block;width:100%;height:auto}.sec-page-stack figcaption{padding:8px 11px;border-top:1px solid var(--line);color:#7b898c;font-size:8px}.sec-solution{overflow:hidden;border:1px solid #b9d1cb;border-radius:12px;background:#fff}.sec-solution>header{display:flex;align-items:center;justify-content:space-between;gap:14px;padding:14px 18px;border-bottom:1px solid #d7e2df;background:#f4f8f6}.sec-solution>header p{margin:0}.sec-solution>header small{color:#607377;font-size:9px}.sec-solution>.reveal{margin-left:18px!important}.sec-solution>.reveal-panel{margin:0 18px 18px!important}.solution-status{margin:0 0 14px;padding:12px 14px;border-radius:8px;font-size:10px;line-height:1.55}.solution-status.supplied,.solution-status.teacher-produced{background:#edf6f2;color:#345e56}.solution-section{padding:13px 0;border-bottom:1px solid var(--line)}.solution-section:last-child{border-bottom:0}.solution-section h3{margin:0 0 8px;color:var(--navy);font:600 17px Georgia}.solution-section ul{display:grid;gap:9px;margin:0;padding-left:19px;color:#40565b;font-size:12px;line-height:1.62}.solution-pages{gap:10px}.sec-acknowledgement{padding:13px 15px;border-top:1px solid var(--line);color:#758689;font-size:9px;line-height:1.5}
@media(max-width:700px){.sec-topic-links>div{grid-template-columns:1fr}.sec-source-banner{flex-direction:column}.sec-source-banner h2{font-size:24px}.sec-source-banner>span{white-space:normal}.sec-topic-links header{align-items:flex-start;flex-direction:column}.sec-solution>header{align-items:flex-start;flex-direction:column}.sec-solution>.reveal{margin-left:14px!important}.sec-solution>.reveal-panel{margin-inline:14px!important}}

/* Version 38 audit repairs: readable teaching labels and safe stale links */
.teaching-block p{font-size:14px}.teaching-block>header,.diagram-head span{font-size:12px;letter-spacing:.08em}.diagram-head b{font-size:14px}.physics-diagram figcaption{font-size:13px}.route-not-found{display:flex;align-items:center;gap:12px;margin-bottom:22px;padding:14px 18px;border:1px solid #e1c78c;border-radius:10px;background:#fff9eb;color:#6c5a2d}.route-not-found strong{font-size:15px}.route-not-found span{font-size:14px}
@media(min-width:901px){#lesson-nav a{font-size:12px;min-height:39px}#lesson-nav>p{font-size:11px}.side-head small{font-size:12px}}

/* Keep the shared sidebar tabs tappable and the selected panel scrollable on mobile Safari. */
.nav-tabs button{touch-action:manipulation;-webkit-tap-highlight-color:transparent}
@media(max-width:900px){.side-head,.nav-tabs{flex:0 0 auto}.nav-tabs{position:relative;z-index:1}#course-nav,#lesson-nav{flex:1 1 0;height:0;-webkit-overflow-scrolling:touch}}

/* Keep the complete mobile drawer below the measured two-row header. */
@media(max-width:900px){.sidebar,.nav-collapsed .sidebar{top:var(--site-header-height,116px);bottom:0}.nav-open .scrim{top:var(--site-header-height,116px);bottom:0}}

/* Multi-panel textbook graphics: each causal stage stays readable on its own. */
.teaching-story{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:14px;padding:16px;background:#eef3f1}.teaching-panel{overflow:hidden;border:1px solid #cbd8d4;border-radius:12px;background:#fff}.teaching-panel header{display:flex;align-items:center;gap:9px;padding:11px 14px;border-bottom:1px solid var(--line);background:#f8faf8}.teaching-panel header span{width:25px;height:25px;display:grid;place-items:center;border-radius:50%;background:var(--teal);color:#fff;font-size:12px;font-weight:800}.teaching-panel header b{color:var(--navy);font-size:14px}.teaching-panel svg{width:100%;height:auto;max-height:none!important;padding:10px}.teaching-panel p{margin:0;padding:0 14px 14px;color:#53696e;font-size:13px;line-height:1.55}.story-figure>figcaption{font-size:13px}.story-figure .teaching-svg{min-width:0!important}.physics-diagram svg[viewBox="0 0 960 1120"]{max-height:none}
@media(max-width:760px){.teaching-story{grid-template-columns:1fr;padding:10px}.teaching-panel header b{font-size:15px}.teaching-panel p{font-size:14px}}
.lesson-progress,.diagram-placeholder{border:1px solid #d6e0df;border-radius:12px;background:#f7faf9;color:#526a70;padding:1rem 1.1rem}
.lesson-progress{min-height:2.5rem;display:flex;align-items:center}
.diagram-placeholder{min-height:9rem;display:grid;place-items:center;margin:1rem 0}

/* Secondary links to optional third-party exam practice. */
.studyclix-resource{display:grid;grid-template-columns:1fr auto;align-items:center;gap:6px 18px;margin:22px 0 4px;padding:14px 16px;border:1px solid #d4dfdc;border-radius:10px;background:#fbfcfc;color:#53696e}.studyclix-resource div{display:grid;gap:3px}.studyclix-resource span{color:#708184;font-size:9px;font-weight:800;letter-spacing:.08em;text-transform:uppercase}.studyclix-resource b{color:var(--navy);font:600 16px Georgia}.studyclix-resource p{margin:0;font-size:13px;line-height:1.45}.studyclix-resource a{padding:8px 10px;border:1px solid #b9d1cb;border-radius:7px;color:var(--teal);font-size:11px;font-weight:800;text-decoration:none;white-space:nowrap}.studyclix-resource a:hover,.studyclix-resource a:focus-visible{background:var(--teal-pale);text-decoration:underline}.studyclix-resource small{grid-column:1/-1;color:#708184;font-size:11px;line-height:1.45}
@media(max-width:600px){.studyclix-resource{grid-template-columns:1fr}.studyclix-resource a{justify-self:start}.studyclix-resource small{grid-column:auto}}

/* Guided PhET links: useful enrichment without loading third-party iframes into lessons. */
.interactive-exploration{display:grid;gap:14px;margin:22px 0;padding:20px;border:1px solid #aacbc4;border-radius:13px;background:linear-gradient(135deg,#f1f8f5,#fff);color:#40575c}.interactive-exploration header{display:flex;align-items:flex-start;justify-content:space-between;gap:20px}.interactive-exploration h2{margin:2px 0 0;color:var(--navy);font:600 24px/1.2 Georgia}.interactive-exploration header a{flex:0 0 auto;padding:10px 12px;border-radius:8px;background:var(--teal);color:#fff;font-size:14px;font-weight:800;text-decoration:none}.interactive-exploration header a:hover,.interactive-exploration header a:focus-visible{background:#11655f;text-decoration:underline}.exploration-purpose{margin:0;font-size:15px;line-height:1.6}.exploration-tasks{padding:15px 17px;border:1px solid #d3e2de;border-radius:9px;background:#fff}.exploration-tasks>b,.exploration-question>b{color:var(--navy);font-size:14px}.exploration-tasks ol{display:grid;gap:7px;margin:10px 0 0;padding-left:22px;font-size:14px;line-height:1.5}.exploration-question{padding:13px 15px;border-left:4px solid var(--teal);background:#eaf5f1}.exploration-question p{margin:5px 0 0;font-size:15px;line-height:1.55}.interactive-exploration>small{color:#64797d;font-size:12px;line-height:1.5}
@media(max-width:650px){.interactive-exploration{padding:16px}.interactive-exploration header{align-items:stretch;flex-direction:column}.interactive-exploration header a{align-self:flex-start}.interactive-exploration h2{font-size:22px}}

.lesson-quick-checks{display:grid;gap:10px;margin:24px 0;padding:20px;border:1px solid #bfd2cd;border-radius:12px;background:#f8fbf9}.lesson-quick-checks h2{margin:0 0 4px;color:var(--navy);font:600 24px Georgia}.lesson-quick-checks details{border-top:1px solid var(--line);padding-top:10px}.lesson-quick-checks summary{display:flex;align-items:flex-start;gap:10px;color:var(--navy);font-size:15px;font-weight:700;line-height:1.45;cursor:pointer}.lesson-quick-checks summary span{flex:0 0 24px;height:24px;display:grid;place-items:center;border-radius:50%;background:var(--teal);color:#fff;font-size:12px}.lesson-quick-checks details p{margin:10px 0 2px 34px;color:#50676c;font-size:14px;line-height:1.55}

/* Classroom Display is a public, device-local presentation preference. */
.teacher:not(.classroom-display) .source-prose p,.teacher:not(.classroom-display) .source-list ul{font-size:14px}.teacher:not(.classroom-display) .source-subheading h2{font-size:26px}
@media(max-width:900px){.classroom-action{position:fixed;left:12px;bottom:14px;z-index:14;box-shadow:0 6px 20px #17313a25}.teacher:not(.classroom-display) .lesson-title h1{font-size:44px}.classroom-display .lesson-title h1{font-size:48px}}
@media(max-width:560px){.teacher:not(.classroom-display) .lesson-title h1{font-size:38px}.classroom-display .lesson-title h1{font-size:42px}}
.definitions-page{max-width:1180px;margin:0 auto;padding:clamp(1.5rem,4vw,4rem)}
.definitions-hero{max-width:780px;margin-bottom:1.5rem}.definitions-hero h1{margin:.2rem 0 .65rem}.definitions-hero>p:last-child{font-size:1.08rem;line-height:1.65;color:var(--muted)}
.definitions-jumps{display:flex;gap:.55rem;flex-wrap:wrap;padding:1rem 0 2rem;border-bottom:1px solid var(--line)}.definitions-jumps button{padding:.55rem .8rem;border:1px solid var(--line);border-radius:999px;background:var(--paper);color:var(--teal);font:inherit;font-weight:700;font-size:.9rem;cursor:pointer}.definitions-jumps button:hover,.definitions-jumps button:focus-visible{border-color:var(--teal);background:var(--soft)}
.definitions-group{padding:2.25rem 0;border-bottom:1px solid var(--line);scroll-margin-top:5rem}.definitions-group>header{margin-bottom:1rem}.definitions-group h2{margin:.2rem 0;font-family:var(--serif);font-size:clamp(1.55rem,3vw,2.15rem);color:var(--ink)}
.definition-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:.85rem}.definition-card{min-width:0;padding:1rem 1.1rem;border:1px solid var(--line);border-left:4px solid var(--teal);border-radius:12px;background:#fff;box-shadow:0 3px 12px rgba(18,52,61,.04)}.definition-card h3{margin:0 0 .45rem;color:var(--ink);font-size:1.06rem}.definition-wording{line-height:1.55;color:var(--ink)}.definition-wording ol{margin:.35rem 0 0;padding-left:1.45rem}.definition-wording li+li{margin-top:.35rem}.definition-detail{margin-top:.75rem;padding-top:.65rem;border-top:1px solid var(--line)}.definition-detail>b{display:block;margin-bottom:.25rem;color:var(--teal);font-size:.78rem;letter-spacing:.09em;text-transform:uppercase}.definition-detail .formula{margin:0;padding:.2rem 0;text-align:left;font-size:1.05rem}.definition-detail p{margin:0}
@media(max-width:720px){.definitions-page{padding:1.25rem}.definition-grid{grid-template-columns:1fr}.definitions-jumps{gap:.4rem}.definitions-jumps button{font-size:.82rem}}
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.search-page-form,.search-result{background:white}.search-page-form input{background:var(--bg)}.search-page-form button{background:var(--teal)}.search-kind,.search-result a{color:var(--teal)}
@media(max-width:900px){.topbar{height:auto;min-height:68px;grid-template-columns:auto 1fr;gap:.45rem .8rem;padding:8px 14px}.topbar .brand{grid-column:2}.breadcrumb{display:none}.site-search{grid-column:1/-1;width:100%;max-width:none;margin-left:0}.sidebar{top:116px}.workspace{padding-top:116px}.search-results-head{display:block}.search-results-head p{margin-top:.3rem}}
@media(max-width:560px){.brand small,.breadcrumb{display:none}.search-page-form>div{display:block}.search-page-form button{width:100%;margin-top:.6rem}.search-page{padding:1rem}.search-result{padding:1rem}}
@media(min-width:901px){.topbar{grid-template-columns:auto 220px minmax(140px,1fr) minmax(260px,390px);gap:12px}.site-search{width:100%}}
.loading{min-height:100vh;display:grid;place-items:center}
.concept-page{max-width:900px;margin:0 auto;padding:36px 24px 70px;color:var(--navy)}
.concept-heading{margin-bottom:24px}.concept-heading h1{font:600 clamp(32px,4vw,46px) Georgia,serif;margin:8px 0 12px}.concept-heading>p:last-child{max-width:700px;color:#50666b;font-size:16px;line-height:1.6}
.concept-setup,.concept-card,.concept-resume{background:#fff;border:1px solid var(--line);border-radius:17px;padding:26px;box-shadow:0 8px 30px #17313a0a;margin:18px 0}
.concept-setup h2,.concept-card h2{font:600 clamp(23px,3vw,30px) Georgia,serif;line-height:1.3;margin:6px 0 22px}
.concept-setup label{display:block;font-size:15px;font-weight:650;color:var(--navy);margin-bottom:18px}
.concept-setup select{display:block;margin-top:7px;width:100%;max-width:540px;min-height:47px;border:1px solid #9db5b7;border-radius:9px;padding:10px 12px;font:inherit;background:#fff;color:var(--navy)}
.concept-options{border:0;padding:0;margin:0}.concept-options legend{font-size:14px;font-weight:700;margin:0 0 10px}
.concept-option{display:flex;gap:13px;align-items:center;padding:13px 15px;margin:9px 0;min-height:49px;border:1px solid #bdcccb;border-radius:10px;cursor:pointer;font-size:16px;line-height:1.45;background:#fff}
.concept-option:has(input:checked){border:2px solid var(--teal);background:#eaf5f1;padding:12px 14px}.concept-option:focus-within{outline:2px solid var(--teal);outline-offset:2px}.concept-option input{accent-color:var(--teal);width:18px;height:18px;flex:none}.concept-options:disabled .concept-option{cursor:default}
.concept-actions{display:flex;gap:12px;align-items:center;flex-wrap:wrap;margin-top:20px}.concept-actions button,.concept-primary,.concept-review-link{display:inline-flex;align-items:center;justify-content:center;min-height:44px;padding:10px 16px;border-radius:9px;border:1px solid var(--teal);background:#fff;color:var(--teal);font:650 15px system-ui,sans-serif;text-decoration:none;cursor:pointer}
.concept-actions button:hover,.concept-review-link:hover{background:#eaf5f1}.concept-actions .concept-primary,.concept-primary{color:#fff;background:var(--teal)}.concept-actions .concept-primary:hover,.concept-primary:hover{background:#125b57}
.concept-notice{margin-top:20px;padding:17px 19px;border-radius:11px;border-left:4px solid var(--teal);background:#eaf5f1;font-size:16px;line-height:1.5}.concept-notice h3{font:700 18px system-ui,sans-serif;margin:0 0 7px}.concept-notice p{margin:0}.concept-notice.hint{border-color:#a57821;background:#fff8e8}.concept-notice.review{border-color:#a75848;background:#fff2ee}.concept-notice.neutral{border-color:#769298;background:#f4f7f7}
.concept-summary-group{margin:22px 0}.concept-summary-group h3{font:600 22px Georgia,serif}.concept-summary-row{display:flex;gap:12px;align-items:center;justify-content:space-between;border-bottom:1px solid var(--line);padding:13px 0;font-size:15px;line-height:1.5}.concept-summary-row .concept-review-link{flex:none}.concept-back-link{display:inline-block;margin:16px 0;color:var(--teal);font-weight:700}.concept-review-focus{outline:3px solid #c58930;outline-offset:5px;border-radius:5px;scroll-margin-top:90px}
@media(max-width:620px){.concept-page{padding:22px 14px 45px}.concept-setup,.concept-card,.concept-resume{padding:19px 16px}.concept-summary-row{align-items:flex-start;flex-direction:column}.concept-summary-row .concept-review-link{width:100%;box-sizing:border-box}.concept-actions>*{flex:1 1 auto}}
.course-practice-grid{grid-template-columns:repeat(3,minmax(0,1fr));gap:11px}.course-practice-card{grid-template-columns:auto minmax(0,1fr);align-content:start;padding:14px 13px;gap:10px;min-width:0}.course-practice-card>span{width:35px;height:35px;font-size:19px}.course-practice-card h2{font-size:19px}.course-practice-card p:last-child{font-size:13px}.course-practice-card>b{align-self:end;font-size:13px}
.concept-fraction{display:inline-grid;vertical-align:middle;line-height:1.05;text-align:center;font-size:.86em;margin:0 .12em;white-space:nowrap}.concept-fraction span:first-child{border-bottom:1px solid currentColor;padding:0 .16em .1em}.concept-fraction span:last-child{padding:.1em .16em 0}
.concept-graph{max-width:440px;margin:0 0 22px;padding:8px 12px;border:1px solid #d6e4e2;border-radius:10px;background:#fafdfc}.concept-graph svg{display:block;width:100%;height:auto}.concept-axis{fill:none;stroke:#52676c;stroke-width:2}.concept-zero{fill:none;stroke:#a5b3b6;stroke-width:1.5;stroke-dasharray:4 4}.concept-line{fill:none;stroke:#08746d;stroke-width:3;stroke-linecap:round;stroke-linejoin:round}.concept-alternative{fill:none;stroke:#a06d33;stroke-width:2;stroke-dasharray:5 3}.concept-axis-label{fill:#354e53;font:11px system-ui,sans-serif}
@media(max-width:1050px){.course-practice-grid{grid-template-columns:repeat(2,minmax(0,1fr))}}@media(max-width:760px){.course-practice-grid{grid-template-columns:1fr}.course-practice-card{padding:16px}.concept-card h2{font-size:clamp(20px,5vw,26px)}.concept-option{font-size:15px;padding:12px}.concept-notice{overflow-wrap:anywhere}.concept-graph{box-sizing:border-box;width:100%;max-width:440px}}
#course-nav .nav-search{margin-bottom:7px}.nav-revision-group{margin-bottom:13px}.nav-revision-heading{margin:12px 18px 6px;color:#718583;font-size:10px;font-weight:800;letter-spacing:.12em}#course-nav .nav-revision-tool{min-height:39px;margin:3px 8px;padding:4px 9px}#course-nav a:focus-visible{outline:2px solid var(--teal);outline-offset:2px}
@media(max-width:900px){#course-nav .nav-revision-tool{min-height:44px;padding:7px 9px}.nav-revision-heading{margin-top:14px}}
.topic-revision{margin-top:2rem}.topic-revision-grid{display:grid;grid-template-columns:repeat(2,minmax(0,1fr));gap:12px}.topic-revision-card{display:flex;align-items:flex-start;gap:12px;min-width:0;min-height:130px;width:100%;padding:19px;border:1px solid #b9d1cb;border-radius:14px;background:linear-gradient(135deg,#eaf5f1,#fff);color:var(--ink);text-align:left;text-decoration:none;cursor:pointer}.topic-revision-card:hover,.topic-revision-card:focus-visible{border-color:var(--teal);box-shadow:0 6px 20px #17313a10}.topic-revision-icon{display:grid;flex:none;place-items:center;width:35px;height:35px;border-radius:50%;background:var(--teal);color:#fff;font-size:19px}.topic-revision-copy{display:flex;flex-direction:column;align-items:flex-start;gap:7px;min-width:0;height:100%}.topic-revision-copy strong{color:var(--navy);font:600 19px/1.25 Georgia,serif}.topic-revision-copy>span{font-size:14px;line-height:1.45;color:#52676c}.topic-revision-copy b{margin-top:auto;padding-top:5px;color:var(--teal);font-size:14px}.topic-revision-deck{margin-top:12px}.topic-revision-deck .flashcard-deck{min-width:0}.topic-revision-deck[hidden]{display:none}
@media(max-width:800px){.topic-revision-grid{grid-template-columns:1fr}.topic-revision-card{min-height:105px}}@media(max-width:480px){.topic-revision-card{padding:16px}.topic-revision-copy strong{font-size:18px}}

html{scroll-behavior:auto;scroll-padding-top:calc(var(--site-header-height,68px) + 16px)}
.lesson-accordion,.concept-card{scroll-margin-top:calc(var(--site-header-height,68px) + 16px)}
.lesson-accordion.open>.lesson-accordion-toggle{top:var(--site-header-height,68px)}
/* Minimal optional analytics choice; the study area remains available. */
.cookie-choice{position:fixed;z-index:1000;bottom:1rem;left:1rem;right:1rem;max-width:43rem;margin:auto;padding:1rem 1.2rem;background:#fff;color:#12343f;border:1px solid #abc5c8;border-radius:12px;box-shadow:0 8px 28px #12343f33;font-size:.95rem;line-height:1.45}
.cookie-choice[hidden]{display:none}
.cookie-choice p{margin:0 0 .7rem}.cookie-choice div{display:flex;align-items:center;gap:.6rem;flex-wrap:wrap}.cookie-choice button{padding:.5rem .8rem;border:1px solid #245567;border-radius:6px;background:#fff;color:#12343f;cursor:pointer;font:inherit}.cookie-choice button:last-child{background:#12343f;color:#fff}.cookie-choice a{color:#164d68;text-decoration:underline}
/* Layered model answers for selected extended-response questions */
.layered-answer{display:grid;gap:18px;overflow-wrap:anywhere}.layered-answer section{min-width:0}.core-model-answer{padding-bottom:16px;border-bottom:1px solid var(--line)}.core-model-answer>div{color:#263f46;font-size:1rem;line-height:1.65}.key-points-checklist h3{margin:0 0 10px}.key-points-checklist ul{display:grid;gap:9px;margin:0;padding:0;list-style:none}.key-points-checklist li{position:relative;padding-left:28px;line-height:1.55}.key-points-checklist li::before{content:'✓';position:absolute;left:0;top:.05em;width:19px;height:19px;border:1px solid #79aaa0;border-radius:5px;color:var(--teal);font-size:12px;font-weight:800;text-align:center;line-height:17px}.fuller-explanation{border-top:1px solid var(--line);padding-top:14px}.fuller-explanation summary,.planning-prompts summary{cursor:pointer;color:var(--teal);font-weight:750}.fuller-explanation>div{margin-top:12px;color:#40565b;line-height:1.7}.fuller-explanation p:first-child{margin-top:0}.planning-prompts{margin:14px 0}.layered-attempt{margin-top:18px}.layered-reveal{margin-top:12px!important}
@media(max-width:700px){.layered-answer{gap:14px;padding:14px!important}.core-model-answer>div,.fuller-explanation>div{font-size:.98rem}.key-points-checklist li{padding-left:25px}.layered-attempt textarea{width:100%;max-width:100%;box-sizing:border-box}}
.physics-diagram,.physics-diagram svg,.physics-diagram img{color-scheme:light}.physics-diagram svg,.physics-diagram img{display:block;max-width:100%;height:auto;margin-inline:auto;background:#fff}.physics-diagram .practical-svg{width:100%;max-height:none;overflow:visible}.lesson-accordion-panel .physics-diagram{width:100%;max-width:100%;min-width:0;overflow:hidden}@media(max-width:560px){.physics-diagram .practical-svg{min-width:0;padding:6px 0}.diagram-viewer-canvas img{width:100%;max-width:100%;height:auto}}
.physics-diagram svg text:not([fill]){fill:#17313a;font-family:Arial,sans-serif}.physics-diagram svg .frame,.physics-diagram svg .panel{fill:#fbfcfb;stroke:#c5d5d1;stroke-width:2}.physics-diagram svg .head,.physics-diagram svg .t{font-size:20px;font-weight:800}.physics-diagram svg .label,.physics-diagram svg .l{font-size:16px;font-weight:700}.physics-diagram svg .small,.physics-diagram svg .s{fill:#53696e;font-size:14px}.physics-diagram svg .xs{font-size:12px}.physics-diagram svg .eq{fill:#12343f;font:700 18px Georgia,serif}.physics-diagram svg .wire,.physics-diagram svg .axis,.physics-diagram svg .ray,.physics-diagram svg .line,.physics-diagram svg .thin{fill:none;stroke:#405b61;stroke-width:3}.physics-diagram svg .thin,.physics-diagram svg .axis{stroke-width:2}.physics-diagram svg .beam{fill:none;stroke:#c98724;stroke-width:4}.physics-diagram svg .measure,.physics-diagram svg .flow{fill:none;stroke:#167a72;stroke-width:4}.physics-diagram svg .force{fill:none;stroke:#a9574a;stroke-width:4}.physics-diagram svg .data,.physics-diagram svg .field{fill:none;stroke:#49769d;stroke-width:4}.physics-diagram svg .dash{stroke-dasharray:7 6}.physics-diagram svg .step{fill:#e6f1ee;stroke:#167a72;stroke-width:2}.physics-diagram svg .screen{stroke:#405b61;stroke-width:7}.physics-diagram svg .meter{fill:#fff;stroke:#405b61;stroke-width:3}.physics-diagram svg .component,.physics-diagram svg .load{fill:#fff5df;stroke:#c98724;stroke-width:3}.physics-diagram svg .hot{fill:#fff0ec;stroke:#a9574a;stroke-width:2}.physics-diagram svg .cold{fill:#edf3f8;stroke:#49769d;stroke-width:2}.physics-diagram svg .core{fill:none;stroke:#77898c;stroke-width:24}.physics-diagram svg .coil{fill:none;stroke:#c98724;stroke-width:6}.physics-diagram svg .earth{fill:none;stroke:#16816f;stroke-width:4}.physics-diagram svg .magnetN{fill:#a9574a}.physics-diagram svg .magnetS{fill:#49769d}
.visual-physics-page{max-width:1240px;margin:0 auto;padding:34px clamp(18px,4vw,54px) 70px}.visual-physics-hero{display:flex;align-items:flex-end;justify-content:space-between;gap:32px;padding:30px;border:1px solid #c9ddd8;border-radius:18px;background:linear-gradient(135deg,#f3faf8,#fff)}.visual-physics-hero h1{margin:.15rem 0 .5rem;color:var(--navy);font:600 clamp(2.2rem,5vw,4rem)/1 Georgia}.visual-physics-hero p:last-child{max-width:760px;margin:0;color:#53696e;line-height:1.7}.visual-physics-hero>strong{display:grid;place-items:center;min-width:132px;padding:20px;border-radius:14px;background:var(--navy);color:#fff;font:700 2.2rem/1 Georgia}.visual-physics-hero>strong span{margin-top:7px;font:700 .67rem/1.2 Arial,sans-serif;letter-spacing:.09em;text-transform:uppercase}.visual-category-nav{display:flex;gap:8px;overflow:auto;margin:20px 0 34px;padding-bottom:5px}.visual-category-nav button{flex:0 0 auto;padding:9px 12px;border:1px solid #c6d8d4;border-radius:999px;background:#fff;color:#34545b;font:700 .78rem/1.25 Arial,sans-serif;cursor:pointer}.visual-category-nav button:hover{border-color:var(--teal);background:#f2faf8}.visual-category-nav button:focus-visible{outline:3px solid #72b9ab;outline-offset:2px}.visual-category{scroll-margin-top:88px;margin-top:42px}.visual-category>header{margin-bottom:14px}.visual-category h2{margin:0;color:var(--navy);font:600 clamp(1.55rem,3vw,2.25rem)/1.15 Georgia}.visual-card-grid{display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:17px}.visual-card{overflow:hidden;border:1px solid #d3dfdc;border-radius:14px;background:#fff;box-shadow:0 8px 24px #17313a0c}.visual-card-preview{display:block;width:100%;height:220px;padding:0;border:0;border-bottom:1px solid #e0e8e6;background:#f4f7f6;cursor:zoom-in}.visual-card-preview img{display:block;width:100%;height:100%;object-fit:contain;background:#fff}.visual-card>div{padding:14px}.visual-card>div>span{color:#688087;font-size:.67rem;font-weight:800;letter-spacing:.08em;text-transform:uppercase}.visual-card h3{min-height:2.5em;margin:.4rem 0 .9rem;color:#223e46;font-size:1rem;line-height:1.3}.visual-card-actions{display:flex;align-items:center;justify-content:space-between;gap:8px}.visual-card-actions .open-full-diagram{padding:7px 9px}.visual-card-actions a{color:var(--teal);font-size:.72rem;font-weight:800;text-decoration:none}.visual-lesson-link{display:flex;align-items:center;justify-content:space-between;gap:20px;margin:8px 0 24px;padding:14px 16px;border:1px solid #b9d8d2;border-radius:12px;background:#f2faf8}.visual-lesson-link p{margin:0 0 3px}.visual-lesson-link b{color:#2f4d54;font-size:.9rem}.visual-lesson-link a{flex:0 0 auto;color:var(--teal);font-size:.78rem;font-weight:800;text-decoration:none}@media(max-width:980px){.visual-card-grid{grid-template-columns:repeat(2,minmax(0,1fr))}}@media(max-width:620px){.visual-physics-page{padding:20px 12px 48px}.visual-physics-hero{align-items:flex-start;flex-direction:column;padding:20px}.visual-physics-hero>strong{display:flex;gap:8px;min-width:0;padding:12px 14px;font-size:1.5rem}.visual-physics-hero>strong span{margin:2px 0 0}.visual-card-grid{grid-template-columns:1fr}.visual-card-preview{height:auto;aspect-ratio:4/3}.visual-card h3{min-height:0}.visual-lesson-link{align-items:flex-start;flex-direction:column;gap:8px}}
body .visual-category-nav{flex-wrap:wrap;overflow:visible}.visual-category-nav a{white-space:normal}
.concept-first{margin:0 0 1.25rem;padding:1.1rem 1.2rem;border:1px solid #9fcfc8;border-left:5px solid var(--teal,#0b6f69);border-radius:14px;background:#f3fbf9;color:#173e3a}.concept-first .eyebrow{margin:0 0 .45rem;color:#08655f;font-weight:800;letter-spacing:.08em;text-transform:uppercase}.concept-first>p:last-child{margin:.35rem 0 0;line-height:1.65}.concept-first details{margin:.25rem 0 .75rem;padding:.65rem .8rem;border-radius:10px;background:#fff;border:1px solid #c9e4df}.concept-first summary{cursor:pointer;font-weight:750;color:#154d48}.concept-first details p{margin:.55rem 0 0}
/* Controlled, repeatable mini-practice questions */
.generated-practice{margin:0 22px 22px}.generated-practice .practice-prompt{margin:18px 0 8px}.generated-practice .practice-formula{padding:12px 0 18px;color:#193f54;font:28px Georgia;text-align:center}.generated-practice .input-row{margin:0 0 12px}.generated-practice output{display:block;margin:0}.input-row .practice-again.secondary{border-color:#9ebdb8;background:white;color:var(--teal)}.input-row button:disabled{cursor:default;opacity:.6}@media(max-width:480px){.generated-practice{margin-inline:16px}.generated-practice .input-row label{width:calc(33% - 6px)}.generated-practice .input-row button{width:100%}}
.feedback-upload{display:none!important}