:root{--ink:#0f172a;--muted:#5b6b81;--line:#dbe3ec;--panel:#fff;--panel-soft:#f8fafc;--page:#eef2f7;--hover:#f1f5f9;--accent:#1d4ed8;--accent-hover:#1e40af;--accent-soft:#dbeafe;--red:#dc2626;--blue:#2563eb;--green:#16a34a;--purple:#7c3aed;--grey:#64748b;--radius:10px;color:var(--ink);background:var(--page);font-family:system-ui,-apple-system,Segoe UI,Roboto,sans-serif;font-size:14px;line-height:1.45}*{box-sizing:border-box}body{background:var(--page);margin:0}button,select,input{font:inherit;color:inherit}button{cursor:pointer}button:focus-visible,select:focus-visible,input:focus-visible{outline:2px solid var(--accent);outline-offset:2px}.app{grid-template:"top top top""rail stage side"minmax(0,1fr)/84px minmax(0,1fr) 340px;height:100dvh;display:grid}.app.has-site-header{grid-template-rows:auto auto minmax(0,1fr);grid-template-areas:"nav nav nav""top top top""rail stage side"}.site-header{border-bottom:1px solid var(--line);background:var(--panel);color:var(--ink);flex-wrap:wrap;grid-area:nav;justify-content:space-between;align-items:center;gap:8px 24px;padding:8px 16px;font-size:14px;line-height:1.45;display:flex}.site-identity{flex-wrap:wrap;align-items:center;gap:8px 14px;min-width:0;display:flex}.site-header .brand{min-height:44px;color:var(--ink);margin:0}.site-header .site-home-link{min-height:44px;color:var(--accent);white-space:nowrap;border-radius:8px;justify-content:center;align-items:center;padding:8px 10px;font-weight:600;text-decoration:none;display:inline-flex}.site-home-link:hover,.site-home-link[aria-current]{background:var(--accent-soft)}.site-lab-name{border-left:1px solid var(--line);padding-left:14px;font-weight:600}.site-mode-nav{border:1px solid var(--line);border-radius:var(--radius);background:var(--panel-soft);gap:4px;padding:3px;display:flex}.site-header .site-mode-link{min-height:44px;color:var(--muted);text-align:center;border-radius:7px;justify-content:center;align-items:center;gap:6px;padding:8px 14px;font-weight:600;text-decoration:none;display:inline-flex}.site-mode-link svg{flex-shrink:0}.site-mode-link:hover{background:var(--hover)}.site-header .site-mode-link[aria-current]{background:var(--accent);color:#fff}.topbar{background:var(--panel);border-bottom:1px solid var(--line);flex-wrap:wrap;grid-area:top;align-items:center;gap:10px;min-width:0;padding:8px 14px;display:flex}.experiment-toolbar .lesson-button{text-align:left;min-width:0;max-width:100%;min-height:44px}.experiment-toolbar .lesson-button svg{flex-shrink:0}.experiment-toolbar .brand,.experiment-toolbar .lab-maths-link{min-height:44px}.brand{color:inherit;border-radius:9px;align-items:center;gap:8px;margin-right:6px;padding:2px 6px 2px 2px;font-size:16px;font-weight:700;text-decoration:none;display:flex}.brand:hover{background:var(--hover)}.logo{background:var(--accent);color:#fff;border-radius:8px;place-items:center;width:30px;height:30px;font-size:16px;display:grid}.spacer{flex:1}.lesson-button{border:1px solid var(--line);background:#f8fafc;border-radius:8px;align-items:center;gap:8px;padding:7px 12px;font-weight:600;display:flex}.lesson-button:hover{border-color:var(--accent)}.group{background:#f1f5f9;border-radius:9px;gap:4px;padding:3px;display:flex}.group button{color:#334155;background:0 0;border:0;border-radius:7px;align-items:center;gap:6px;padding:6px 10px;font-weight:600;display:flex}.group button:hover:not(:disabled):not(.on):not(.primary){background:#e2e8f0}.group button:disabled{opacity:.4;cursor:default}.group button.on{background:var(--ink);color:#fff}.group button.primary{background:var(--accent);color:#fff;justify-content:center;min-width:88px}.group button.primary.pulse{animation:1.6s ease-in-out infinite pulse}@keyframes pulse{50%{box-shadow:0 0 0 4px #1d4ed840}}@media (prefers-reduced-motion:reduce){.group button.primary.pulse{animation:none}}.labelled-select{color:#334155;align-items:center;gap:6px;font-weight:600;display:flex}select{border:1px solid var(--line);background:#fff;border-radius:7px;padding:5px 8px}.toolrail{background:var(--panel);border-right:1px solid var(--line);flex-direction:column;grid-area:rail;gap:4px;padding:10px 8px;display:flex;overflow-y:auto}.toolrail button{color:#334155;background:0 0;border:0;border-radius:9px;flex-direction:column;align-items:center;gap:3px;padding:9px 2px;font-size:11px;font-weight:600;display:flex}.toolrail button:hover{background:#f1f5f9}.toolrail button.on{background:var(--accent-soft);color:var(--accent)}.stage{grid-area:stage;min-height:0;position:relative}.sim-canvas{touch-action:none;width:100%;height:100%;display:block}.stage-hint{color:var(--muted);pointer-events:none;white-space:nowrap;font-size:12px;position:absolute;bottom:4px;left:50%;transform:translate(-50%)}.check{align-items:center;gap:8px;margin:8px 4px 4px;font-weight:600;display:flex}.toast{background:var(--ink);color:#fff;border-radius:8px;padding:8px 14px;font-weight:600;position:absolute;bottom:30px;left:50%;transform:translate(-50%);box-shadow:0 6px 20px #0f172a40}.paused-banner{color:#92400e;pointer-events:none;background:#fef3c7;border-radius:999px;padding:6px 14px;font-weight:700;position:absolute;top:26px;left:50%;transform:translate(-50%)}.lab-status{min-height:100vh;color:var(--muted);text-align:center;place-content:center;justify-items:center;gap:12px;padding:24px 16px;font-weight:600;display:grid}.lab-status p{margin:0}.reload-offer{z-index:30;border-radius:var(--radius);background:var(--ink);color:#fff;flex-wrap:wrap;align-items:center;gap:8px 12px;width:max-content;max-width:calc(100vw - 32px);padding:10px 14px;font-weight:600;display:flex;position:fixed;bottom:24px;left:50%;transform:translate(-50%);box-shadow:0 6px 20px #0f172a40}.reload-offer p{margin:0}.sidebar{background:var(--page);border-left:1px solid var(--line);flex-direction:column;grid-area:side;gap:12px;padding:12px;display:flex;overflow-y:auto}.panel{background:var(--panel);border:1px solid var(--line);border-radius:var(--radius);padding:12px 14px}.panel-head{align-items:center;gap:10px;margin-bottom:8px;display:flex}.panel h2{margin:0;font-size:16px}.panel h3{text-transform:uppercase;letter-spacing:.04em;color:var(--muted);margin:14px 0 6px;font-size:12px}.grow{flex:1;min-width:0}.swatch{border:2px solid;border-radius:5px;flex:none;width:18px;height:18px;display:inline-block}.icon-button{border:1px solid var(--line);color:#475569;background:#fff;border-radius:7px;place-items:center;width:28px;height:28px;display:grid}.icon-button:hover{border-color:var(--red);color:var(--red)}.text-button{border:1px solid var(--line);color:var(--accent);background:#fff;border-radius:7px;align-items:center;gap:4px;padding:4px 10px;font-weight:600;display:inline-flex}.text-button:hover{border-color:var(--accent)}.eyebrow{text-transform:uppercase;letter-spacing:.04em;color:var(--muted);margin:10px 0 4px;font-size:12px;font-weight:700}.predict{background:#fffbeb;border:1px solid #fde68a;border-radius:8px;padding:10px 12px}.predict .eyebrow{color:#92400e;margin-top:0}.predict p{margin:0 0 8px}.predict .answer{border-top:1px dashed #fcd34d;margin:8px 0 0;padding-top:8px}.steps{margin:0;padding-left:20px}.steps li{margin-bottom:4px}.big-idea{background:var(--accent-soft);color:#1e3a8a;border-radius:8px;gap:8px;margin-top:12px;padding:10px 12px;font-weight:600;display:flex}.big-idea p{margin:0}.big-idea svg{flex:none;margin-top:2px}.status{border-radius:999px;margin-top:2px;padding:1px 8px;font-size:12px;font-weight:700;display:inline-block}.status-blue{color:#1e40af;background:#dbeafe}.status-red{color:#991b1b;background:#fee2e2}.status-grey{color:#334155;background:#f1f5f9}.status-green{color:#166534;background:#dcfce7}.status-purple{color:#5b21b6;background:#ede9fe}.facts{grid-template-columns:1fr 1fr;gap:6px;margin:0;display:grid}.facts div{background:#f8fafc;border-radius:7px;padding:6px 8px}.facts div.highlight{background:#fef3c7}.facts dt{color:var(--muted);font-size:11px}.facts dd{font-variant-numeric:tabular-nums;margin:0;font-weight:700}.force{margin-bottom:6px}.force-label{justify-content:space-between;font-size:13px;display:flex}.force-label b{font-variant-numeric:tabular-nums}.force small{color:var(--muted)}.force-track{background:#f1f5f9;border-radius:4px;height:8px;overflow:hidden}.force-track div{border-radius:4px;height:100%;transition:width .12s linear}.tone-red div{background:var(--red)}.tone-blue div{background:var(--blue)}.tone-grey div{background:var(--grey)}.tone-green div{background:var(--green)}.tone-purple div{background:var(--purple)}.explain{background:#eff6ff;border-radius:7px;margin:8px 0 0;padding:8px 10px;font-size:13px}.subpanel{background:#f8fafc;border-radius:8px;margin-top:12px;padding:8px 10px}.row{align-items:center;gap:8px;display:flex}.meter{background:#e2e8f0;border-radius:3px;height:6px;margin-top:6px;overflow:hidden}.meter div{background:var(--blue);height:100%}.back-to-lesson{color:var(--accent);background:0 0;border:0;align-self:flex-start;margin-top:-6px;padding:2px 4px;font-weight:600}.hint{color:var(--muted);margin:0 0 8px;font-size:12px}.muted{color:var(--muted)}.footnote{color:var(--muted);margin:0;font-size:12px}.picker{border:0;border-radius:14px;width:min(860px,100vw - 32px);max-height:calc(100vh - 64px);padding:18px;box-shadow:0 24px 60px #0f172a4d}.picker::backdrop{background:#0f172a73}.picker-head{justify-content:space-between;align-items:center;margin-bottom:12px;display:flex}.picker-head h2{margin:0}.picker-grid{grid-template-columns:repeat(auto-fill,minmax(250px,1fr));gap:8px;margin:0;padding:0;list-style:none;display:grid}.picker-grid button{border:1px solid var(--line);text-align:left;background:#fff;border-radius:10px;gap:10px;width:100%;height:100%;padding:10px 12px;display:flex}.picker-grid button:hover{border-color:var(--accent)}.picker-grid button.current{border-color:var(--accent);background:var(--accent-soft)}.picker-grid .number{background:var(--ink);color:#fff;border-radius:50%;flex:none;place-items:center;width:26px;height:26px;font-size:13px;font-weight:700;display:grid}.picker-grid b{display:block}.picker-grid small{color:var(--muted)}@media (width<=1100px){.app{grid-template-columns:72px minmax(0,1fr) 300px}}@media (width<=820px){.app{grid-template:"top""rail""stage"60vh"side"/1fr;height:auto}.app.has-site-header{grid-template-rows:auto auto auto 60vh auto;grid-template-areas:"nav""top""rail""stage""side"}.toolrail{border-right:0;border-bottom:1px solid var(--line);flex-direction:row;overflow-x:auto}.toolrail button{min-width:64px}.sidebar{border-left:0}.stage-hint{white-space:normal;text-align:center;width:calc(100% - 32px)}}.app.no-tools{grid-template-columns:minmax(0,1fr) 340px;grid-template-areas:"top top""stage side"}.app.no-tools.has-site-header{grid-template-areas:"nav nav""top top""stage side"}@media (width<=820px){.app.no-tools{grid-template:"top""stage"60vh"side"/1fr}.app.no-tools.has-site-header{grid-template-rows:auto auto 60vh auto;grid-template-areas:"nav""top""stage""side"}}@media (width<=650px){.site-header{gap:8px;padding:8px 12px}.site-identity{gap:4px 10px;width:100%}.site-header .brand{font-size:15px}.site-header .site-home-link{margin-left:auto}.site-lab-name{border:0;width:100%;padding:0 2px 4px}.site-mode-nav{width:100%}.site-header .site-mode-link{flex:1;padding-inline:8px;font-size:13px}}.home{min-height:100vh}.home-content{max-width:1080px;margin:0 auto;padding:48px 16px}.home-head h1{margin:0 0 6px;font-size:30px}.home-head p{color:var(--muted);margin:0 0 28px;font-size:16px}.lab-grid{grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:14px;margin:0;padding:0;list-style:none;display:grid}.lab-card{border:1px solid var(--line);border-radius:var(--radius);background:var(--panel);flex-direction:column;display:flex;overflow:hidden}.lab-grid .lab-card>button{border:0;border-radius:0;flex:1;height:auto}.lab-practice-link{border-top:1px solid var(--line);color:var(--accent);justify-content:space-between;gap:12px;margin:0 18px;padding:14px 0;font-weight:700;text-decoration:none;display:flex}.lab-practice-link span{font-size:12px}.lab-maths-link{border:1px solid var(--line);color:var(--accent);border-radius:7px;padding:7px 10px;font-weight:600;text-decoration:none}.lab-practice-link:hover,.lab-maths-link:hover{text-decoration:underline}a:focus-visible{outline:2px solid var(--accent);outline-offset:3px}.lab-grid button{border:1px solid var(--line);border-radius:var(--radius);background:var(--panel);text-align:left;flex-direction:column;align-items:flex-start;gap:6px;width:100%;height:100%;padding:18px;display:flex}.lab-grid button:hover{border-color:var(--accent);box-shadow:0 4px 14px #0f172a14}.lab-grid b{font-size:17px}.lab-grid span:not(.lab-icon){color:#334155}.lab-grid small{color:var(--muted);margin-top:auto;padding-top:6px;font-weight:600}.lab-icon{background:var(--accent-soft);width:44px;height:44px;color:var(--accent);border-radius:11px;place-items:center;margin-bottom:4px;display:grid}.materials-grid{grid-template-columns:1fr 1fr;gap:2px;display:grid}.materials-grid button{text-align:left;background:0 0;border:1px solid #0000;border-radius:7px;align-items:center;gap:8px;min-width:0;padding:4px 6px;font-size:12.5px;display:flex}.materials-grid.single{grid-template-columns:1fr}.materials-grid button:hover{background:#f1f5f9}.materials-grid button.on{border-color:var(--accent);background:var(--accent-soft)}.materials-grid small{color:var(--muted);font-variant-numeric:tabular-nums}.slider{margin:10px 0;display:block}.slider-label{justify-content:space-between;margin-bottom:2px;font-size:13px;display:flex}.slider-label b{font-variant-numeric:tabular-nums}.slider input{width:100%}.field{flex-direction:column;gap:4px;margin:10px 0;font-size:13px;display:flex}.segmented{background:#f1f5f9;border-radius:9px;gap:4px;margin:10px 0;padding:3px;display:flex}.segmented button{background:0 0;border:0;border-radius:7px;flex:1;min-width:0;padding:5px 4px;font-weight:600}.segmented button.on{color:var(--accent);background:#fff;box-shadow:0 1px 2px #0f172a1f}.chart{width:100%;height:auto;font-size:10px}.chart text{fill:var(--muted)}.chart .axis{fill:#334155;font-weight:600}.chart .grid{stroke:var(--line);stroke-width:1px}.chart .theory{stroke:var(--blue);stroke-width:1.5px;stroke-dasharray:5 4}.chart .point{fill:var(--purple)}.legend{font-variant-numeric:tabular-nums;flex-direction:column;gap:3px;margin:6px 0 0;padding:0;font-size:12px;list-style:none;display:flex}.legend li{align-items:center;gap:8px;display:flex}.legend-line{border-top:3px solid;width:18px}.legend-line.dashed{border-top-style:dashed}