:root{color-scheme:dark;--bg:#07111f;--panel:#0d1d30;--line:#273343;--text:#e9eef5;--muted:#9baabd;--accent:#50e3c2;--c:#80e0ba}*{box-sizing:border-box}html{scroll-behavior:smooth;scroll-padding-top:24px}body{margin:0;background:var(--bg);color:var(--text);font:16px/1.65 Inter,system-ui,Segoe UI,Arial,sans-serif}a{color:inherit;text-decoration:none}a:hover{color:var(--accent)}button,input,select,textarea{font:inherit}button,.button{display:inline-flex;align-items:center;justify-content:center;gap:18px;min-height:44px;padding:10px 18px;border:1px solid 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6px;min-height:0;border-radius:5px;color:var(--c);border:1px solid color-mix(in srgb,var(--c) 35%,transparent);background:color-mix(in srgb,var(--c) 10%,#101823)}.element:hover{background:color-mix(in srgb,var(--c) 28%,#101823)}.element[aria-pressed=true]{background:color-mix(in srgb,var(--c) 25%,#101823);outline:2px solid var(--c);outline-offset:0;color:var(--c);border-color:var(--c)}.element .z{font-size:10px;line-height:1.2}.element b{font-size:21px;line-height:1.35}.element small{font-size:9px;line-height:1.2}.element.dim{opacity:.2}.grid-label{color:var(--muted);font-size:11px;display:flex;align-items:center;justify-content:center}.legend{display:flex;gap:10px 20px;flex-wrap:wrap;margin-top:22px;font-size:11px;color:var(--muted)}.legend span:before{content:'';display:inline-block;width:8px;height:8px;border-radius:2px;background:var(--c);margin-right:6px}.scroll-hint{font-size:12px;color:var(--muted);margin:0 0 12px}.periodic-panel .fine{font-size:11px;margin:14px 0 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var(--line)}th{color:var(--muted);font-weight:500}.comparison-table td{width:30%}.comparison-table th{width:40%}.trend-elements{display:flex;gap:10px;flex-wrap:wrap;margin:22px 0}.trend-elements button{flex:1;min-width:54px;font-size:22px}.range-label{display:block}.range-label input{width:100%;padding:0;accent-color:var(--accent)}.trend-detail{display:grid;grid-template-columns:1fr 1fr;align-items:center;gap:30px}.trend-detail svg{max-height:250px}.trend-map{display:grid;grid-template-columns:1fr 1fr;gap:16px;margin-top:20px}.trend-arrow{border:1px solid var(--line);border-radius:8px;padding:16px;background:linear-gradient(90deg,#213a34,#12202b);font-size:14px}.practice-grid{display:grid;grid-template-columns:1.2fr 1fr;gap:20px}#build-atom svg{max-height:260px}#build-controls{display:flex;flex-wrap:wrap;gap:12px;margin:20px 0}.shell-control{display:flex;align-items:center;gap:9px;flex:1;background:#0e1723;border-radius:8px;padding:10px;min-width:170px}.shell-control button{padding:4px 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@media(prefers-reduced-motion:reduce){html{scroll-behavior:auto}*,*:before,*:after{animation:none!important;transition:none!important}}

.trend-overview{grid-column:1/-1}.mini-periodic{display:grid;grid-template-columns:repeat(18,1fr);gap:4px;min-width:700px;padding:4px}.mini-periodic span{padding:4px;text-align:center;font-size:12px;border-radius:3px}button,select,input,textarea{font-family:inherit}


/* Bond laboratory extension; base tokens and layout match laboratory 01. */
.atom-grid{display:grid;grid-template-columns:minmax(0,1fr) 38px minmax(0,1fr);gap:16px;align-items:center}.atom-grid article{min-width:0}.atom-grid select{width:100%;margin:6px 0}.atom-grid svg{max-height:260px}.combine{text-align:center;font-size:30px;color:var(--accent)}.preset-row{margin-bottom:20px}.preset-row button{font-size:13px;padding:8px 13px}.en-panel{margin:20px 0;display:grid;grid-template-columns:1.5fr 1fr;gap:20px}.en-panel h3{font-size:20px}.full{grid-column:1/-1;margin:0}.density{display:flex;justify-content:center;align-items:center;gap:20px;flex-wrap:wrap}.density b{font-size:28px}.density>span{font-size:44px;color:var(--accent)}.density small{flex-basis:100%;text-align:center;color:var(--muted);font-size:14px}.bond-stage{min-height:210px;display:grid;place-items:center;overflow:hidden;background:radial-gradient(ellipse,#19393c80,transparent 70%);border-radius:10px}.bond-stage svg{max-height:250px}.ready-atoms,.transfer-model{display:flex;align-items:center;justify-content:center;gap:32px;font-size:42px}.ready-atoms sup{display:block;font-size:14px;color:var(--accent)}.ready-atoms>span:nth-child(2){font-size:22px;color:var(--muted)}.transfer-model{width:90%}.transfer-path{position:relative;width:40%;height:50px;border-bottom:1px dashed #526779}.transfer-path i{position:absolute;color:var(--accent);font-size:18px;animation:transfer 1s ease-in-out both;animation-delay:var(--delay)}@keyframes transfer{from{left:0;opacity:.1}to{left:90%;opacity:1}}.ion-result{display:flex;align-items:center;justify-content:center;gap:20px;flex-wrap:wrap;width:100%;font-size:38px;color:var(--accent)}.ion-result>span:first-child{color:#89b8f0}.ion-result .attraction{font-size:14px;color:var(--muted)}.formula{font-size:32px;font-weight:700;margin:15px 0;letter-spacing:1px}.simulation .fine{margin:20px 0 0}.simulation h3{overflow-wrap:anywhere}.simulation #bond-next{display:flex;gap:12px;flex-wrap:wrap}.forming{animation:appear 1s ease-in-out}@keyframes appear{from{opacity:.25;transform:scale(.92)}to{opacity:1;transform:scale(1)}}.two-col{display:grid;grid-template-columns:minmax(0,1fr) minmax(0,1fr);gap:24px;align-items:center}.two-col>*{min-width:0}.lattice-panel{margin-top:18px}.lattice-panel canvas,#metal-canvas{width:100%;height:auto;touch-action:none;cursor:grab;background:radial-gradient(ellipse,#213c4655,transparent 70%);border-radius:10px}.lattice-panel canvas:active{cursor:grabbing}.lattice-panel .fine{margin:14px 0 0}#compare-body td{min-width:150px}#compare-body td:last-child{min-width:280px}#samples{margin-bottom:20px}#sample-tests button{font-weight:500}#observations{padding:20px 0;min-height:90px}#observations li{margin-bottom:9px}.circuit{display:flex;align-items:center;justify-content:center;gap:10px;min-height:120px;border:1px solid var(--line);border-radius:10px;padding:15px;margin:20px 0}.wire{height:2px;flex:1;background:#53657c}.lamp{font-size:40px;color:#687185}.circuit.on .lamp{color:#ffe38a;text-shadow:0 0 20px #ffe38a}.circuit.on .wire{background:var(--accent)}#charge-model{font-size:18px;max-width:45%;text-align:center}.shift-model{height:215px;padding:15px 10px;overflow:hidden;background:#071521;border-radius:10px;margin-bottom:20px}.shift-model>div{display:flex;justify-content:center;gap:10px;transition:transform .7s,margin .7s}.shift-model span{width:34px;height:34px;display:grid;place-items:center;background:#20425a;border-radius:50%;color:#a9d4ff;margin:3px 0;font-size:23px}.ionic-shift>div:nth-child(odd)>span:nth-child(even),.ionic-shift>div:nth-child(even)>span:nth-child(odd){background:#245746;color:#b4f6dc}.shifted>div:nth-child(-n+2){transform:translateX(44px)}.ionic-shift.shifted>div:nth-child(3){margin-top:20px}.metal-shift{background:radial-gradient(ellipse,#25504870,#071521)}.metal-shift span{background:#5a4331;color:#f5d1ac}.electron-bank{border:1px solid var(--line);border-radius:10px;padding:22px;align-self:stretch;margin:16px 0}.electron-bank h3{font-size:32px;color:var(--accent);margin-bottom:5px}.electron-bank p{color:var(--muted);font-size:14px}.electron{border-radius:50%;padding:6px;width:44px;min-width:44px;color:var(--accent)}.electron[aria-pressed=true]{outline:2px solid var(--accent)}#build-progress svg{max-height:230px}.research-fields{display:grid;grid-template-columns:1fr 1fr;gap:20px;margin:20px 0}.research-fields select{display:block;width:100%;margin:7px 0 0;font-size:14px}select[aria-invalid=true]{border-color:#ed9c92;outline:1px solid #ed9c92}.task fieldset legend{font-size:17px;font-weight:700;margin-bottom:14px}.task fieldset label{font-size:15px;min-height:44px}.task fieldset input{min-height:22px}.hero-bond{display:flex;align-items:center}.hero-bond svg{width:46%;height:auto}.hero-bond>span{font-size:30px;color:var(--accent)}.hero-crystal{display:grid;grid-template-columns:repeat(4,1fr);gap:8px;max-width:220px;margin:0 auto 20px;transform:skewY(-8deg)}.hero-crystal span{font-size:16px;border:1px solid #50e3c266;border-radius:8px;padding:7px;color:var(--accent)}.hero-crystal span:nth-child(even){color:#8bbbf1;border-color:#8bbbf166}.panel-top b{font-size:24px;color:var(--accent)}.sources a,.accordion-grid a{text-decoration:underline;color:var(--accent)}#metal-detail{color:var(--muted)}.task-feedback:empty{display:none}
@media(max-width:768px){.atom-grid{grid-template-columns:1fr}.combine{line-height:1}.two-col,.en-panel{grid-template-columns:1fr}.atom-grid .stats{grid-template-columns:1.4fr 1fr 1fr}.atom-grid svg{max-height:230px}.research-fields{grid-template-columns:1fr}.circuit{gap:5px;padding:10px}.circuit>span:first-child{font-size:12px}.shift-model span{width:30px;height:30px}.shift-model>div{gap:8px}.shifted>div:nth-child(-n+2){transform:translateX(38px)}.en-panel h3{font-size:19px}.hero{padding-bottom:25px}.ready-atoms,.transfer-model{font-size:34px;gap:18px}.ion-result{font-size:32px;gap:12px}.table-scroll{margin-top:16px}.section-nav a{min-height:35px;display:flex;align-items:center}#sample-answer{display:block;width:100%;margin:8px 0 12px}.panel-top{flex-wrap:wrap;gap:8px}.bond-stage{min-height:180px}.simulation .toolbar button{flex:1}header img{max-width:100%}.breadcrumbs{overflow-wrap:anywhere}.task fieldset{min-width:0}}
@media(prefers-reduced-motion:reduce){.transfer-path i{position:static;margin:0 5px}.forming{opacity:1;transform:none}}

.model-legend{font-size:14px;margin:14px 0}.ion-shells{color:var(--muted);font-size:16px}