:root{--paper:#fbfcf9;--white:#fff;--ink:#182e34;--muted:#5e6e70;--line:#d7e0dc;--accent:#245f76;--tint:#eaf2f1;--soft:#f0f4ee;--field:#edf3f3;--diagram-ink:#28566f;--fuel:#9a6b34;--heat:#ae5738;--neutrons:#6e62a2;--error:#a2332b;--success:#28624c;--font:"Helvetica Neue",Helvetica,Arial,sans-serif;--mono:ui-monospace,SFMono-Regular,Consolas,monospace;--radius:8px;--space:clamp(22px,4vw,64px);--content:1240px;--reading:690px;--focus:3px solid #32758d;--layout-gap:clamp(30px,4vw,64px);--motion-quick:.16s;--motion-ease:cubic-bezier(.2,.7,.3,1);--line-strong:#afc3bb;--surface-hover:#f3f7f3;--shadow-card:0 5px 18px #182e340b;--bubble:#e3efeb;--shadow-bubble:0 3px 3px #182e3440;--radius-card:14px;--space-xs:8px;--space-sm:12px;--space-md:20px;--space-lg:28px;--space-xl:40px;--space-section:56px;--type-label:12px;--type-small:14px;--type-body:16px;--type-card:25px;--leading-copy:1.75;--graphite:#7e8a83;--graphite-light:#d4dbd7;--diagram-water:#dcebef;--diagram-water-line:#8aabb8;--diagram-material:#e8decd;--art-line:#687f7a;--art-muted:#c7d4cd;--brand-blue:#365baa;--brand-violet:#6d529a;--brand-wash:#eef1f8;--brand-line:#bdc8dd}.ui-icon{width:var(--icon-size,20px);height:var(--icon-size,20px);vertical-align:middle;stroke-width:1.7px;flex-shrink:0;display:inline-block}.choice-option{border:1px solid var(--line-strong);border-radius:var(--radius);background:var(--white);cursor:pointer;align-items:flex-start;gap:12px;margin:0 0 10px;padding:14px;font-size:15px;line-height:1.5;display:flex}.choice-option:has(input:checked){border-color:var(--accent);background:var(--tint)}.choice-option:focus-within{outline:var(--focus);outline-offset:3px}.choice-option input{width:18px;height:18px;accent-color:var(--accent);flex:none;margin:3px 0 0}.choice-option input:focus-visible{outline:none}.review-choices .choice-option input:disabled{opacity:1}@media (prefers-reduced-motion:no-preference){.choice-option{transition:border-color var(--motion-quick),background-color var(--motion-quick)}}.control-option{border:1px solid var(--line-strong);border-radius:var(--radius);background:var(--white);min-height:44px;color:var(--ink);font:inherit;cursor:pointer;padding:9px 12px;font-size:13px;line-height:1.4}.control-option:hover{border-color:var(--accent);color:var(--accent)}.control-option[aria-pressed=true]{border-color:var(--accent);background:var(--tint);color:var(--ink)}@media (prefers-reduced-motion:no-preference){.control-option{transition:border-color var(--motion-quick),background-color var(--motion-quick),color var(--motion-quick)}}.action-link{justify-content:center;align-items:center;gap:var(--space-xs);min-height:44px;font-size:var(--type-small);color:var(--accent);border-radius:var(--radius);font-weight:500;line-height:1.4;text-decoration:none;display:inline-flex}.action-link:hover{color:var(--ink);text-decoration:none}.action-link--text{padding:8px 2px}.action-link--back{color:var(--muted);margin-bottom:var(--space-sm);justify-content:flex-start;padding-block:8px}.ui-section-heading{align-items:end;gap:var(--space-lg);margin-bottom:var(--space-lg)}.ui-section-heading .eyebrow{margin-bottom:var(--space-sm)}.ui-section-heading h2{font-size:clamp(27px,3vw,34px)}.ui-section-heading .section-description{max-width:600px;font-size:var(--type-body);line-height:var(--leading-copy);color:var(--muted);margin-top:var(--space-sm)}.ui-section-heading>.action-link{flex-shrink:0}.resource-grid{gap:var(--space-md);grid-template-columns:repeat(3,minmax(0,1fr));margin:0;padding:0;list-style:none;display:grid}.resource-grid>li{min-width:0;display:flex}.resource-grid--two{grid-template-columns:repeat(2,minmax(0,1fr))}.resource-card{border:1px solid var(--line);border-radius:var(--radius-card);background:var(--white);width:100%;min-width:0;color:var(--ink);flex-direction:column;text-decoration:none;display:flex;overflow:hidden}.resource-card:hover,.resource-card:focus-visible{background:var(--white);border-color:var(--line-strong);box-shadow:var(--shadow-card);text-decoration:none}.resource-card-art{background:var(--soft);border-bottom:1px solid var(--line);justify-content:center;align-items:center;min-width:0;display:flex;overflow:hidden}.resource-card-art svg{width:100%;height:175px;display:block}.resource-card-copy{padding:var(--space-md);min-width:0}.resource-card-meta{color:var(--muted);font-size:var(--type-label);margin-bottom:var(--space-sm);line-height:1.5}.resource-card-title{gap:var(--space-sm);font-size:var(--type-card);justify-content:space-between;align-items:start;line-height:1.3;display:flex}.resource-card-title>span{min-width:0}.resource-card-title>.ui-icon{color:var(--accent);margin-top:5px}.resource-card-description{font-size:15px;line-height:var(--leading-copy);color:var(--muted);margin-top:var(--space-sm)}.resource-card:hover .resource-card-title,.resource-card:focus-visible .resource-card-title{color:var(--accent);text-decoration:none}.resource-card--wide{grid-template-columns:210px minmax(0,1fr);align-items:stretch;display:grid}.resource-card--wide .resource-card-art{border-bottom:0;border-right:1px solid var(--line)}.resource-card--wide .resource-card-art svg{height:100%;min-height:150px;max-height:220px}.resource-card--wide .resource-card-copy{padding:var(--space-lg);align-self:center}.resource-card--wide .resource-card-title{font-size:28px}.topic-illustration{--art-color:var(--fuel);--art-fill:#e1cfb5}.topic-illustration--decay{--art-color:var(--accent);--art-fill:#bdd2d6}.topic-illustration--pwr{--art-color:var(--heat);--art-fill:#e8c8b2}.topic-illustration--cycle{--art-color:#607963;--art-fill:#d2dfcf}.topic-illustration .art-halo{fill:var(--art-fill);opacity:.22}.topic-illustration .art-guide{fill:none;stroke:var(--art-muted);stroke-width:.7px;stroke-dasharray:2 5;opacity:.7}.topic-illustration .art-line{fill:none;stroke:var(--art-line);stroke-width:1.5px;stroke-linecap:round;stroke-linejoin:round}.topic-illustration .art-wash{fill:var(--paper);stroke:var(--art-line);stroke-width:1.5px}.topic-illustration .art-solid{fill:var(--art-fill);stroke:var(--art-color);stroke-width:1.5px}.topic-illustration .art-highlight{fill:var(--paper);stroke:var(--art-color);stroke-width:1.3px}.topic-illustration .art-atom{fill:var(--art-color);stroke:var(--art-color);stroke-width:1.5px}.topic-illustration .art-empty{fill:var(--paper);stroke:var(--art-line);stroke-width:1.5px;opacity:.7}.topic-illustration .art-cool{fill:none;stroke:var(--accent);stroke-width:4px}.topic-illustration .art-hot{fill:none;stroke:var(--heat);stroke-width:3px}.topic-illustration .art-fuel{fill:none;stroke:var(--fuel);stroke-width:4px}.topic-illustration .art-vessel{fill:#edf3f3;fill-opacity:.65;stroke:var(--art-line);stroke-width:1.5px}.worksheet-resource{align-items:center;gap:var(--space-md);border-top:1px solid var(--line);padding-block:var(--space-lg);grid-template-columns:48px minmax(0,1fr) auto;display:grid}.resource-symbol{background:var(--soft);border-radius:var(--radius);width:48px;height:48px;color:var(--accent);justify-content:center;align-items:center;display:flex}.worksheet-resource h3{font-size:23px;line-height:1.3}.worksheet-resource p{color:var(--muted);margin-top:var(--space-xs);font-size:15px;line-height:var(--leading-copy);max-width:650px}.worksheet-resource nav{align-items:center;gap:var(--space-sm);display:flex}.interest-list{margin:0;padding:0;list-style:none}.interest-list li{align-items:start;gap:var(--space-sm);padding-block:var(--space-sm);font-size:18px;line-height:1.55;display:flex}.interest-list .ui-icon{color:var(--accent);margin-top:3px}.interest-list strong{font-weight:500}.interest-list p{margin-top:var(--space-xs);color:var(--muted);font-size:16px;line-height:var(--leading-copy)}.interest-list--detailed li+li{border-top:1px solid var(--line);margin-top:var(--space-xs);padding-top:var(--space-md)}.topic-link{gap:var(--space-md);border-top:1px solid var(--line);padding-block:var(--space-lg);grid-template-columns:40px minmax(0,1fr) 20px;align-items:start;text-decoration:none;display:grid}.topic-link>.ui-icon:first-child{color:var(--accent);margin-top:3px}.topic-link>.ui-icon:last-child{color:var(--muted);margin-top:4px}.topic-link h3{margin-top:var(--space-xs);font-size:24px;line-height:1.35}.topic-link p{margin-top:var(--space-sm);color:var(--muted);font-size:13px}.topic-link:hover,.topic-link:focus-visible{text-decoration:none}.topic-link:hover h3,.topic-link:focus-visible h3{color:var(--accent);text-decoration:none}@media (prefers-reduced-motion:no-preference){.resource-card{transition:border-color var(--motion-quick),box-shadow var(--motion-quick)}.resource-card-title>.ui-icon,.action-link--text>.ui-icon{transition:transform var(--motion-quick) var(--motion-ease)}.resource-card:hover .resource-card-title>.ui-icon,.action-link--text:hover>.ui-icon{transform:translate(2px)}}@media (width<=1000px){.resource-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:16px}.resource-card-title{font-size:23px}.resource-card-copy{padding:18px}.worksheet-resource{grid-template-columns:44px minmax(0,1fr)}.worksheet-resource nav{grid-column:2}.resource-card--wide{grid-template-columns:170px minmax(0,1fr)}}@media (width<=760px){.ui-section-heading{align-items:start;gap:var(--space-xs);margin-bottom:var(--space-md);flex-direction:column}.resource-grid,.resource-grid--two{gap:var(--space-sm);grid-template-columns:1fr}.resource-card,.resource-card--wide{flex-direction:column;gap:0;padding:0;display:flex}.resource-card-art,.resource-card--wide .resource-card-art{border:0;border-bottom:1px solid var(--line);border-radius:0;align-self:stretch}.resource-card-art svg,.resource-card--wide .resource-card-art svg{width:100%;height:88px;min-height:0;max-height:none}.resource-card-copy,.resource-card--wide .resource-card-copy{width:100%;padding:var(--space-md)}.resource-card-title,.resource-card--wide .resource-card-title{gap:var(--space-sm);font-size:23px}.resource-card-title>.ui-icon{width:17px;height:17px;margin-top:5px}.resource-card-description{margin-top:10px;font-size:14px;line-height:1.65}.resource-card-meta{margin-bottom:8px}.worksheet-resource{padding-block:var(--space-md);gap:12px 16px}.worksheet-resource h3{font-size:22px}.worksheet-resource nav{gap:var(--space-sm);flex-wrap:wrap;grid-column:1/-1}.topic-link{gap:var(--space-sm);grid-template-columns:28px minmax(0,1fr) 18px}.topic-link h3{font-size:22px}.interest-list li{font-size:16px}}@media print{.resource-card{break-inside:avoid;box-shadow:none}.resource-card-art{display:none}.resource-card--wide{display:block}.ui-icon{display:none}}.concept-figure svg{overflow:visible}.concept-figure svg text{font:17px var(--font);fill:var(--ink)}.concept-figure svg .concept-small{fill:var(--muted);font-size:14px}.concept-vessel{fill:var(--paper);stroke:var(--art-line);stroke-width:1.8px}.concept-material{fill:var(--diagram-material);stroke:var(--fuel);stroke-width:1.8px}.concept-water{fill:var(--diagram-water);stroke:var(--diagram-water-line);stroke-width:1.3px}.concept-fuel{fill:none;stroke:var(--fuel);stroke-width:6px;stroke-linecap:round}.concept-flow{fill:none;stroke:var(--accent);stroke-width:2px;stroke-linecap:round;stroke-linejoin:round}.concept-heat{fill:none;stroke:var(--heat);stroke-width:2.4px;stroke-linecap:round;stroke-linejoin:round}.concept-recovery{fill:none;stroke:var(--fuel);stroke-width:1.8px;stroke-dasharray:5 5;stroke-linejoin:round}.concept-vapor{fill:var(--paper);stroke:var(--diagram-water-line);stroke-width:1.4px}.concept-bubbles{fill:var(--paper);stroke:var(--diagram-water-line);stroke-width:1.5px}.concept-molecules{fill:var(--accent);opacity:.65}.concept-neutron{fill:none;stroke:var(--neutrons);stroke-width:2px;stroke-dasharray:4 3}.concept-dashed{stroke-dasharray:3 5}.concept-sun{fill:none;stroke:var(--fuel);stroke-width:2px}.concept-figure svg.cycle-route text,.concept-figure svg.solar-circuit text{font-size:20px}.concept-figure svg.cycle-route .concept-small,.concept-figure svg.solar-circuit .concept-small{font-size:16px}.cycle-route,.solar-circuit{max-width:430px;margin:auto}.mechanism-pair,.storage-stages{gap:var(--space-lg);grid-template-columns:1fr 1fr;display:grid}.mechanism-pair>div,.storage-stages>div{min-width:0}.mechanism-pair h3,.storage-stages h3{font-size:20px;line-height:1.3}.mechanism-pair svg,.storage-stages svg{width:100%;height:auto;display:block}.mechanism-pair p{font-size:15px;line-height:var(--leading-copy);margin-top:var(--space-sm)}.concept-figure .storage-explanation{font-size:15px;line-height:var(--leading-copy);margin-top:var(--space-md)}.decay-stages{gap:var(--space-md);text-align:center;grid-template-columns:repeat(3,minmax(0,1fr));display:grid}.decay-stages p{justify-content:center;align-items:center;min-height:44px;font-size:14px;display:flex}.decay-stages svg{width:100%;max-width:100px;margin:var(--space-sm) auto;display:block}.decay-stages strong{font-size:28px;font-weight:500;display:block}.parent-atom{fill:var(--accent);background:var(--accent);stroke:var(--accent)}.daughter-atom{fill:var(--paper);background:var(--paper);stroke:var(--art-line)}.concept-key{justify-content:center;gap:var(--space-sm) var(--space-lg);margin-top:var(--space-md);flex-wrap:wrap;font-size:13px;display:flex}.concept-key span{align-items:center;gap:var(--space-xs);display:flex}.concept-key i{border:1px solid var(--art-line);border-radius:50%;width:12px;height:12px}@media (width<=760px){.mechanism-pair{grid-template-columns:1fr}.mechanism-pair>div+div{border-top:1px solid var(--line-strong);padding-top:var(--space-md)}.mechanism-pair svg{max-width:360px;margin:auto}.storage-stages{gap:var(--space-sm)}.storage-stages h3{font-size:18px}.decay-stages{gap:var(--space-xs)}}.accident-diagram{max-width:480px;margin:auto}.concept-figure svg.accident-diagram text{font-size:20px}.concept-figure svg.accident-diagram .concept-small{font-size:16px}@media (width<=380px){.concept-figure svg.accident-diagram .concept-small{font-size:18px}}.graphite-surround{fill:var(--graphite-light);stroke:var(--art-line);stroke-width:1.2px}.rod-connector{fill:none;stroke:var(--art-line);stroke-width:2px;stroke-dasharray:3 3}.rod-absorber{fill:var(--ink);background:var(--ink)}.rod-graphite{fill:var(--graphite);background:var(--graphite)}.rod-changed{fill:none;stroke:var(--heat);stroke-width:2px;stroke-dasharray:4 3}.core-enclosure{fill:var(--paper);stroke:var(--art-line);stroke-width:3px}.upper-cover{fill:var(--art-line)}.reference-conditions{color:var(--muted);margin-bottom:var(--space-md);font-size:13px}.cross-section-reference dl{margin:0}.cross-section-reference dl>div{justify-content:space-between;align-items:center;gap:var(--space-sm);border-top:1px solid var(--line-strong);padding-block:var(--space-sm);display:flex}.cross-section-reference dt a{align-items:center;gap:var(--space-xs);text-underline-offset:3px;font-size:16px;text-decoration:underline;display:inline-flex}.cross-section-reference dt small{color:var(--muted);font-size:13px;display:block}.cross-section-reference dd{font-variant-numeric:tabular-nums;text-align:right;margin:0;font-size:19px}.cross-section-reference dd span{color:var(--muted);font-size:12px;display:block}.beam-plane{fill:none;stroke:var(--art-line);stroke-width:1.5px;stroke-dasharray:4 4}.concept-figure[data-beam-model]>svg{max-width:560px;margin-inline:auto}.beam-right{fill:none;stroke:var(--accent);stroke-width:3.5px;stroke-linejoin:round}.beam-left{fill:none;stroke:var(--neutrons);stroke-width:3.5px;stroke-linejoin:round}.beam-left-dot{fill:var(--neutrons)}.beam-results{gap:var(--space-md);grid-template-columns:1fr 1fr;display:grid}.beam-results p{margin:0}.beam-results span,.beam-results small{font-size:13px;display:block}.beam-results span{min-height:2.8em;line-height:1.4}.beam-results strong{font-variant-numeric:tabular-nums;font-size:36px;font-weight:500;line-height:1.4;display:block}.beam-results small{color:var(--muted)}.question-context{flex-wrap:wrap;align-items:flex-start;gap:8px;margin-top:16px;display:flex}.investigation-background{max-width:690px}.investigation-background .question-context{grid-template-columns:repeat(2,minmax(0,1fr));align-items:stretch;gap:8px;margin-top:10px;display:grid}.investigation-background .question-context:not(:has(.concept-note[open])) .concept-note:last-child:nth-child(odd),.investigation-background .question-context:has(.concept-note[open]) .concept-note{grid-column:1/-1}.investigation-background .concept-note summary{min-height:46px}.investigation-background .concept-note:not([open]) summary{height:100%}.concept-note{border:1px solid var(--line-strong);border-radius:var(--radius);background:var(--paper);min-width:0;max-width:100%;margin-top:0}.concept-note summary{min-height:40px;color:var(--accent);cursor:pointer;align-items:center;gap:8px;padding:8px 12px;font-size:14px;line-height:1.35;list-style:none;display:flex}.concept-note summary::-webkit-details-marker{display:none}.concept-note summary:after{content:none}.concept-note summary .ui-icon{flex:none}.concept-note-title{align-items:center;gap:9px;min-width:0;display:inline-flex}.investigation-background .concept-note summary{grid-template-columns:minmax(0,1fr) auto;display:grid}.investigation-background .concept-note-title{grid-template-columns:auto minmax(0,1fr);display:grid}.concept-note--visual .concept-note-title>.ui-icon{color:var(--brand-blue)}.concept-note[open]{flex-basis:100%}.concept-note[open] summary .concept-note-toggle{transform:rotate(45deg)}@media (prefers-reduced-motion:no-preference){.concept-note-toggle{transition:transform var(--motion-quick) var(--motion-ease)}.concept-note{transition:border-color var(--motion-quick),background-color var(--motion-quick)}}.concept-note-body{border-top:1px solid var(--line);padding:12px;font-size:15px;line-height:1.6}.concept-note-body a{color:var(--accent);text-underline-offset:3px;align-items:center;gap:4px;margin-top:10px;font-size:13px;text-decoration:underline;display:inline-flex}.concept-note--visual{border-color:var(--brand-line);background:var(--white)}.concept-note--visual[open] .concept-note-body{grid-template-columns:minmax(0,1fr) minmax(0,1fr);align-items:center;gap:20px;padding:16px;display:grid}.background-visual{border-radius:var(--radius);background:var(--field);min-width:0;padding:10px}.background-visual svg{width:100%;height:auto;display:block}.background-visual svg text{fill:var(--ink);font:15px var(--font)}.background-visual svg .visual-small{font-size:13px}.background-visual .visual-guide{fill:none;stroke:var(--brand-line);stroke-width:1px;stroke-dasharray:3 6}.background-visual .visual-path,.background-visual .visual-arrow,.background-visual .visual-north,.background-visual .visual-steam{fill:none;stroke:var(--accent);stroke-width:2px;stroke-linecap:round;stroke-linejoin:round}.background-visual .visual-dot{fill:var(--neutrons)}.background-visual .visual-dot-muted{fill:var(--muted)}.background-visual .visual-nucleus,.background-visual .visual-fragment{fill:var(--fuel)}.background-visual .visual-water{fill:#d4e7ed;stroke:var(--accent);stroke-width:1.5px}.background-visual .visual-rod{fill:var(--ink)}.background-visual figcaption{color:var(--muted);margin-top:4px;font-size:12px;line-height:1.4}.background-visual figcaption a{color:inherit;font-size:inherit;margin:0}.background-visual--location{background:#e9f1ee}.background-visual svg.chernobyl-map{overflow:hidden}.chernobyl-map .map-land-ukraine{fill:#e7efdf}.chernobyl-map .map-land-belarus{fill:#d5e2d3;stroke:#a1b4a4;stroke-width:1px}.chernobyl-map .map-river{fill:none;stroke:#8fb5c3;stroke-width:2px;stroke-linecap:round;stroke-linejoin:round}.background-visual svg .map-country{fill:#63796a;letter-spacing:.05em;font-size:13px}.background-visual svg .map-water-label{fill:#4c7481;font-size:14px}.background-visual svg .map-place-label{fill:var(--ink);font-size:15px;font-weight:500}.background-visual svg .map-north-label{font-size:14px}.chernobyl-map .map-place-halo{fill:var(--paper);opacity:.85}.chernobyl-map .map-place{fill:var(--brand-blue)}.chernobyl-map .map-city{fill:var(--ink)}.chernobyl-map .map-label-line,.chernobyl-map .map-north{fill:none;stroke:var(--brand-blue);stroke-width:1.4px}@media (width<=760px){.concept-note--visual[open] .concept-note-body{grid-template-columns:1fr;gap:12px}}@media (width<=380px){.investigation-background .concept-note summary{gap:6px;padding-inline:7px;font-size:13px}.investigation-background .concept-note-title{gap:6px}.investigation-background .concept-note-title>span{min-width:0}.investigation-background .concept-note-title>.ui-icon{width:15px;height:15px}.investigation-background .concept-note-toggle{width:12px;height:12px}}@media print{.concept-note[open]{break-inside:avoid}}.background-visual .visual-neutron{fill:none;stroke:var(--neutrons);stroke-width:2px;stroke-linecap:round;stroke-linejoin:round}.background-visual .visual-fuel{fill:var(--diagram-material);stroke:var(--fuel);stroke-width:1.8px}.background-visual .visual-fuel-detail{stroke:var(--fuel);stroke-width:1.2px}.background-visual .visual-turbine{fill:var(--diagram-material);stroke:var(--heat);stroke-width:1.8px;stroke-linejoin:round}.background-visual .visual-shaft{stroke:var(--art-line);stroke-width:2px}.background-visual .visual-steam{stroke:var(--heat)}.rod-comparison .rod-highlight{fill:none;stroke:var(--heat);stroke-width:2.5px}.rod-comparison .rod-callout{fill:none;stroke:var(--heat);stroke-width:1.8px;stroke-linejoin:round}.concept-figure .rod-comparison .rod-callout-label{fill:var(--heat);font-size:16px}.explorer-choices{gap:var(--space-xs);margin-top:var(--space-md);flex-wrap:wrap;display:flex}.explorer-choices button{flex:130px;min-height:44px}.explorer-readings{min-height:100px;margin-top:var(--space-md)}.explorer-readings p{font-size:16px;line-height:1.7}.loop-chain{grid-template-columns:1fr 50px 1fr 50px 1fr;align-items:center;gap:8px;display:grid}.loop-stage{border-radius:var(--radius);border:1px solid var(--line);min-width:0;padding:30px 8px 12px;position:relative}.loop-stage svg{width:100%;height:auto}.loop-stage strong,.loop-stage>span:not(.cover-gas),.salt-sketches strong,.salt-sketches span{text-align:center;font-size:14px;line-height:1.5;display:block}.loop-stage>span:not(.cover-gas),.salt-sketches span{color:var(--muted);margin-top:6px}.cover-gas{top:8px;text-align:center;color:var(--muted);font-size:12px;position:absolute;inset-inline:4px}.loop-transfer{color:var(--heat);text-align:center;font-size:12px}.salt-sketches{gap:var(--space-sm);grid-template-columns:repeat(3,minmax(0,1fr));display:grid}.salt-sketches>div{border:1px solid var(--line);border-radius:var(--radius);padding:10px}.salt-sketches svg{width:100%;max-width:180px;margin:auto;display:block}.concept-explorer[data-explorer-active=primary] [data-stage=primary],.concept-explorer[data-explorer-active=intermediate] [data-stage=intermediate],.concept-explorer[data-explorer-active=water] [data-stage=water],.concept-explorer[data-explorer-active=pressure] [data-stage=pressure],.concept-explorer[data-explorer-active=chemistry] [data-stage=chemistry],.concept-explorer[data-explorer-active=freezing] [data-stage=freezing]{border-color:var(--accent);background:var(--paper)}.absorption-assumptions{color:var(--muted);margin-bottom:var(--space-md);font-size:14px;line-height:1.7}.absorption-comparison{gap:var(--space-md);margin-bottom:var(--space-lg);display:grid}.absorption-comparison h3{justify-content:space-between;gap:12px;margin-bottom:10px;font-size:18px;display:flex}.absorption-comparison h3 span{color:var(--muted);font-size:14px;font-weight:400}.absorption-track{border:1px solid var(--line-strong);background:var(--paper);border-radius:4px;height:24px;overflow:hidden}.absorption-track>span{background:var(--neutrons);height:100%;display:block}.absorption-comparison p{margin-top:8px;font-size:14px}.conductor-neutrons label{flex-wrap:wrap;justify-content:space-between;gap:8px;font-size:14px;display:flex}.conductor-neutrons output{color:var(--muted)}@media (prefers-reduced-motion:no-preference){.absorption-track>span{transition:width var(--motion-quick)}}@media (width<=600px){.loop-chain{grid-template-columns:minmax(0,1fr);gap:10px}.loop-stage{padding:26px 12px 14px}.loop-stage svg{max-width:140px;margin:auto;display:block}.salt-sketches{grid-template-columns:minmax(0,1fr)}.salt-sketches>div{grid-template-columns:85px minmax(0,1fr);align-items:center;column-gap:12px;display:grid}.salt-sketches svg{grid-row:1/3}.salt-sketches strong,.salt-sketches span{text-align:left}.explorer-readings{min-height:170px}.loop-stage{grid-template-columns:80px minmax(0,1fr);align-items:center;gap:4px 12px;padding:12px;display:grid}.loop-stage svg{grid-area:1/1/4;max-width:80px}.loop-stage .cover-gas{text-align:left;grid-area:1/2;position:static}.loop-stage strong,.loop-stage>span:not(.cover-gas){text-align:left;grid-column:2;margin-top:0}.loop-transfer{height:24px;font-size:0;transform:none}.loop-transfer:after{content:"Heat ↓";font-size:14px}}@media (width>=601px){.loop-chain{align-items:stretch}.loop-stage{flex-direction:column;display:flex}.loop-stage strong{justify-content:center;align-items:center;min-height:42px;display:flex}.loop-transfer{justify-content:center;align-items:center;display:flex}}*{box-sizing:border-box}html{scrollbar-gutter:stable;scroll-padding-top:24px}body{background:var(--paper);color:var(--ink);font:16px/1.65 var(--font);-webkit-font-smoothing:antialiased;margin:0}button,input,textarea,select{font:inherit}button,summary{cursor:pointer}a{color:inherit;text-decoration:none}a:hover{color:var(--accent)}:focus-visible{outline:var(--focus);outline-offset:5px}[hidden]{display:none!important}button:disabled,input:disabled,textarea:disabled{opacity:.5;cursor:not-allowed}h1,h2,h3,p,figure{margin:0}h1,h2,h3{letter-spacing:-.035em;text-wrap:pretty;font-weight:500;line-height:1.15}h1{font-size:clamp(38px,4.8vw,64px)}h2{font-size:clamp(28px,3vw,38px)}h3{font-size:24px}p+p{margin-top:18px}.wrap{width:min(var(--content),calc(100% - var(--space)*2));margin-inline:auto}.narrow{width:min(var(--reading),calc(100% - var(--space)*2));margin-inline:auto}.eyebrow,.record-label{font:12px/1.5 var(--mono);letter-spacing:.015em;color:var(--muted)}.sr-only{clip:rect(0,0,0,0);white-space:nowrap;width:1px;height:1px;position:absolute;overflow:hidden}.skip-link{z-index:100;background:var(--white);padding:12px 16px;position:fixed;top:-100px;left:20px}.skip-link:focus{top:12px}.site-header{justify-content:space-between;align-items:center;gap:24px;min-height:86px;display:flex}.site-name{flex-shrink:0;margin-left:-12px;display:block}.site-name img{object-fit:contain;mix-blend-mode:multiply;width:195px;height:65px;display:block}.site-header nav{align-items:center;gap:var(--space-xs);font-size:14px;display:flex}.site-header nav a{min-width:44px;min-height:44px;color:var(--muted);justify-content:center;align-items:center;padding:8px 12px;display:inline-flex;position:relative}.site-header nav a:hover,.site-header nav a[aria-current]{color:var(--ink);text-decoration:none}.site-header nav a[aria-current]{font-weight:600}.site-header nav a[aria-current]:after{content:"";background:var(--brand-blue);border-radius:50%;width:6px;height:6px;position:absolute;bottom:3px;left:calc(50% - 3px)}.site-footer{margin-top:var(--space-section);padding-block:var(--space-lg);border-top:1px solid var(--line);justify-content:space-between;align-items:center;gap:var(--space-lg);color:var(--muted);font-size:14px;display:flex}.footer-identity{color:var(--ink);font-size:16px;font-weight:500}.site-footer nav{gap:4px var(--space-sm);flex-wrap:wrap;display:flex}.site-footer a{align-items:center;min-height:44px;display:inline-flex}.site-footer nav a{border-radius:var(--radius);padding:8px 12px}.site-footer nav a:hover,.site-footer nav a[aria-current]{color:var(--ink);text-decoration:none}.site-footer nav a[aria-current]{font-weight:600}.button{justify-content:center;align-items:center;gap:var(--space-xs);border:1px solid var(--ink);border-radius:var(--radius);background:var(--ink);color:var(--white);min-height:48px;padding:12px 19px;font-size:14px;line-height:1.45;text-decoration:none;display:inline-flex}.button:hover{background:var(--accent);color:var(--white);text-decoration:none}.button.secondary{background:var(--white);border-color:var(--line-strong);color:var(--ink)}.button.secondary:hover{background:var(--tint)}.text-button{gap:var(--space-xs);text-align:left;min-height:44px;color:var(--accent);background:0 0;border:0;align-items:center;padding:10px 0;font-size:14px;display:inline-flex}.text-button:hover{color:var(--ink)}.page-intro{padding-block:46px 36px}.page-intro h1{max-width:850px;margin-top:16px}.page-intro>p:last-child{max-width:680px;margin-top:22px;font-size:19px;line-height:1.75}.section-heading{justify-content:space-between;align-items:baseline;gap:30px;margin-bottom:24px;display:flex}.section-heading h2{font-size:29px}.section-heading p{color:var(--muted);font-size:14px}.back-link{color:var(--muted);padding-block:12px;font-size:13px;display:inline-block}.source-locator{color:var(--muted);font-size:12px!important;line-height:1.75!important}.article-connections{border-top:1px solid var(--line);margin-top:40px;padding-top:28px}.article-connections>h2{margin-bottom:22px;font-size:27px}.article-practice{margin-top:24px}details{margin-top:14px}summary{justify-content:space-between;align-items:center;gap:var(--space-md);color:var(--accent);min-height:44px;padding-block:10px;font-size:14px;list-style:none;display:flex}summary::-webkit-details-marker{display:none}summary::marker{content:""}summary:after{content:"";background:currentColor;flex-shrink:0;width:18px;height:18px;display:block;mask:url("data:image/svg+xml,%3csvg%20xmlns='http://www.w3.org/2000/svg'%20width='24'%20height='24'%20viewBox='0%200%2024%2024'%20fill='none'%20stroke='currentColor'%20stroke-width='2'%20stroke-linecap='round'%20stroke-linejoin='round'%20%3e%3cpath%20d='M5%2012h14'%20/%3e%3cpath%20d='M12%205v14'%20/%3e%3c/svg%3e") 50%/contain no-repeat}details[open]>summary:after{transform:rotate(45deg)}summary:hover{color:var(--ink)}details>p{margin-top:12px}label{margin-bottom:8px;font-size:14px;display:block}input[type=text],textarea,select{border:1px solid var(--line-strong);border-radius:var(--radius);background:var(--white);width:100%;color:var(--ink);padding:12px 14px;display:block}select{appearance:none;background-image:url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' width='16' height='16' viewBox='0 0 24 24' fill='none' stroke='%23182e34' stroke-width='1.8' stroke-linecap='round' stroke-linejoin='round'%3E%3Cpath d='m6 9 6 6 6-6'/%3E%3C/svg%3E");background-position:right 16px center;background-repeat:no-repeat;background-size:16px;padding-right:44px}textarea{resize:vertical;line-height:1.7}input[aria-invalid=true]{border-color:var(--error)}input[type=range]{width:100%;min-height:30px;accent-color:var(--accent);margin:12px 0 24px}input[type=radio],input[type=checkbox]{accent-color:var(--accent)}fieldset{border:0;margin:24px 0 0;padding:0}legend{padding-right:12px;font-size:14px}.practice-problem{border-bottom:1px solid var(--line);padding-block:28px}.practice-problem h3,.reasoning-prompt{letter-spacing:-.015em;margin:12px 0 20px;font-size:20px;line-height:1.6;display:block}.answer-row{align-items:start;gap:12px;display:flex}.answer-row input{min-width:0;max-width:250px;min-height:48px}.answer-row .button{white-space:nowrap}.answer-feedback{color:var(--error);margin-top:12px;font-size:14px}.answer-feedback:empty{display:none}.answer-feedback[data-correct=true]{color:var(--success)}.problem-help{grid-template-columns:1fr 1fr;gap:20px;display:grid}.problem-help p,.practice-problem details p{color:var(--muted);font-size:14px;line-height:1.75}.attempt-history{color:var(--muted);margin-top:12px;font-size:12px}.practice-footer{flex-wrap:wrap;justify-content:space-between;align-items:center;gap:16px;margin-top:24px;font-size:14px;display:flex}.practice-footer a{color:var(--accent)}.notice{background:var(--tint);border-radius:var(--radius);overflow-wrap:anywhere;margin-top:20px;padding:16px 20px;font-size:14px}.storage-warning{z-index:1000;border-radius:var(--radius);max-width:760px;color:var(--error);background:#fff3ef;border:1px solid #d8b0a9;margin:auto;padding:16px 20px;font-size:14px;position:fixed;inset:auto 20px 16px;box-shadow:0 8px 30px #182e341a}.lesson-heading{max-width:1040px;padding-block:28px 24px}.lesson-heading h1{max-width:800px;margin-top:12px}.lesson-shell{max-width:1040px}.lesson-panel{margin-top:48px;scroll-margin-top:24px}.lesson-panel.narrow{width:100%;max-width:var(--reading);margin-inline:0}.lesson-panel>h2{margin-bottom:18px;font-size:29px}.lesson-panel>p{font-size:18px;line-height:1.8}.halving-sequence{border-block:1px solid var(--line);letter-spacing:-.035em;font-variant-numeric:tabular-nums;justify-content:space-between;align-items:center;gap:8px;margin-block:28px;padding-block:28px;font-size:clamp(26px,4vw,42px);display:flex}.halving-sequence small{font-size:15px}.halving-sequence>span:nth-child(2n){color:var(--muted);font-size:18px}.equation{white-space:nowrap;padding-inline:6px;font-family:Georgia,serif;display:inline-block}.model-heading{justify-content:space-between;align-items:baseline;gap:28px;display:flex}.model-heading h2{font-size:29px}.model-heading>p{max-width:340px;color:var(--muted);font-size:14px;line-height:1.75}.model-grid{border:1px solid var(--line);border-radius:var(--radius-card);background:var(--field);grid-template-columns:270px minmax(0,1fr);gap:48px;margin-top:28px;padding:30px;display:grid}.model-controls label{justify-content:space-between;gap:14px;display:flex}.model-controls output{font-variant-numeric:tabular-nums}.model-result{flex-direction:column;margin-top:14px;display:flex}.model-result strong{letter-spacing:-.045em;font-variant-numeric:tabular-nums;font-size:58px;font-weight:500;line-height:1.1}.model-result>span{margin-top:12px;font-size:14px}.model-result small{color:var(--muted);margin-top:8px;font-size:12px}.model-limit{color:var(--muted);margin-top:18px;font-size:13px!important}.decay-figure svg{width:100%;display:block}.decay-figure figcaption{color:var(--muted);margin-top:16px;font-size:12px}.grid-lines path{stroke:#c9d6d3;fill:none;stroke-width:1px}.axis-labels text{font:12px var(--font);fill:var(--muted)}.chart-area{fill:#d7e7e8}.chart-line{fill:none;stroke:var(--accent);stroke-width:3px}.chart-guide{fill:none;stroke:#819eaa;stroke-width:1px;stroke-dasharray:4 5}.chart-point{fill:var(--accent);stroke:var(--white);stroke-width:3px}.nowrap{white-space:nowrap}.worksheet{padding-top:30px}.print-actions{justify-content:space-between;align-items:center;gap:20px;margin-bottom:36px;font-size:14px;display:flex}.worksheet h1{margin:18px 0 24px;font-size:clamp(34px,4vw,49px)}.worksheet>p{font-size:15px;line-height:1.8}.worksheet-name{flex-wrap:wrap;justify-content:space-between;gap:16px;margin-top:30px;font-size:13px;display:flex}.worksheet-problem{break-inside:avoid;margin-top:34px}.worksheet-problem h2{margin-top:12px;font-size:19px;line-height:1.6}.worksheet-problem li,.worksheet-solution{font-size:16px;line-height:1.8}.worksheet-solution{margin-top:16px}.working-lines{background:repeating-linear-gradient(transparent 0,transparent 31px,var(--line) 32px);height:130px;margin-top:14px}.worksheet>.no-print,.worksheet .source-locator{margin-top:30px}pre{white-space:pre-wrap;overflow-wrap:anywhere;background:var(--soft);border-radius:var(--radius);max-height:400px;font:12px/1.75 var(--mono);padding:18px;overflow:auto}dialog{border:1px solid var(--line);border-radius:var(--radius-card);background:var(--paper);width:min(720px,100% - 32px);max-height:calc(100dvh - 40px);color:var(--ink);margin:auto;padding:32px;overflow:auto}dialog:not(.investigation-tool){position:fixed;inset:0}dialog::backdrop{background:#18333c55}dialog>p{color:var(--muted);margin-top:18px;font-size:14px}.table-scroll{margin-top:24px;overflow-x:auto}.investigation-table{border-collapse:collapse;text-align:left;width:100%;font-size:13px;line-height:1.7}.investigation-table th,.investigation-table td{vertical-align:top;border-bottom:1px solid var(--line);padding:13px 14px 13px 0}.investigation-table thead th{color:var(--muted);font-size:11px;font-weight:500}.investigation-table tbody th{min-width:100px;font-weight:500}.technical-figure{border:1px solid var(--line);border-radius:var(--radius-card);background:var(--field);min-width:0;margin-top:28px;padding:28px}.technical-figure>svg{width:100%;height:auto;display:block}.technical-figure :where(svg text){font:14px var(--font);fill:var(--ink)}.technical-figure svg text[fill=\#fff]{fill:#fff}.technical-figure svg .small-label{font-size:12px}.technical-figure .diagram-title{margin-bottom:16px;font-size:14px;font-weight:500}.technical-figure figcaption{color:var(--muted);margin-top:18px;font-size:12px;line-height:1.75}.technical-figure figcaption a{text-underline-offset:3px;text-decoration:underline}.pwr-loops{container-type:inline-size}.pwr-loops .loop-small{display:none}.circuit-heading{color:var(--muted);justify-content:space-between;gap:25px;margin-bottom:5px;font-size:11px;display:flex}.primary-pipe{fill:none;stroke:#427995;stroke-width:5px}.vessel{fill:#f8fafb;stroke:#6d808a;stroke-width:2px}.exchanger-vessel{fill:#edf2f5}.fuel-rods{stroke:#a66b3d;stroke-width:6px}.steam-pipe{fill:none;stroke:#b76a46;stroke-width:4px;stroke-dasharray:9 4}.secondary-return{fill:none;stroke:#728992;stroke-width:4px}.turbine{fill:#f1e4db;stroke:#9f7255;stroke-width:2px}.condenser{fill:#e2ebef;stroke:#728992;stroke-width:2px}.diagram-line{stroke:#6d808a;stroke-width:3px}.pipe-arrow{fill:none;stroke:#2c5f79;stroke-width:2px}.steam-arrow{fill:none;stroke:#9d5333;stroke-width:2px}.heat-arrow{fill:none;stroke:#a66b3d;stroke-width:3px}.circuit-boundary{fill:none;stroke:#bac7ce;stroke-width:1px}@container (width<=540px){.pwr-loops .loop-wide,.pwr-loops .circuit-heading{display:none}.pwr-loops .loop-small{max-width:430px;margin:auto;display:block}}.fuel-geometry-panels{grid-template-columns:1fr 1fr;gap:32px;display:grid}.fuel-geometry-panels>div{min-width:0}.fuel-geometry-panels svg{width:100%;height:auto;display:block}.fuel-geometry svg .small-label{font-size:14px}.figure-step{align-items:baseline;gap:12px;margin-bottom:24px;font-size:13px;display:flex}.figure-step>span{color:var(--muted);font-variant-numeric:tabular-nums;font-size:11px}.geometry-leaders{fill:var(--diagram-ink);stroke:var(--diagram-ink);stroke-width:.8px}.geometry-leaders path{fill:none}.conduction-sketch{padding-block:15px 10px}.conduction-boundaries{width:var(--solid-length,100%);justify-content:space-between;min-width:180px;font-size:12px;display:flex}.conduction-track{align-items:center;height:100px;display:flex}.solid-path{width:var(--solid-length,100%);height:var(--solid-thickness,58px);color:#263f4d;background:linear-gradient(#a3b5bf,#e7edef 40%,#b1c1ca);border-block:1px solid #8499a5;place-items:center;min-width:180px;font-size:13px;display:grid;position:relative}.solid-path:before,.solid-path:after{content:"";background:#a66b3d;width:7px;position:absolute;inset:-5px auto -5px 0}.solid-path:after{background:var(--diagram-ink);inset:-5px 0 -5px auto}.model-input-grid{grid-template-columns:1fr 1fr;gap:25px;margin-top:20px;display:grid}.model-input-grid label{justify-content:space-between;align-items:start;gap:15px;font-size:14px;display:flex}.model-input-grid output{white-space:nowrap}.model-input-grid input[type=range]{margin-bottom:15px}.model-input-grid select{padding:9px 40px 9px 9px;font-size:12px}.model-measure{flex-direction:column;display:flex}.model-measure strong{letter-spacing:-.03em;font-size:38px;font-weight:500;line-height:1.2}.model-measure>span{color:var(--muted);margin-top:6px;font-size:12px}.technical-figure .model-equation{overflow-wrap:anywhere;margin-top:18px;font-family:Georgia,serif;font-size:15px;line-height:1.8}.technical-figure .axis-labels text{fill:var(--muted);font-size:12px}.field-options{gap:var(--space-xs);grid-template-columns:1fr 1fr;margin-top:18px;display:grid}.field-options button:not([aria-pressed=true]){color:var(--muted)}.field-readout{font-size:14px}.field-readout p{border-bottom:1px solid var(--line);justify-content:space-between;gap:18px;margin:0;padding-block:8px;display:flex}.field-readout strong{white-space:nowrap;font-weight:500}.field-key{color:var(--muted);flex-wrap:wrap;justify-content:space-between;gap:12px;font-size:13px;display:flex}.field-key>span{align-items:center;gap:8px;display:flex}.field-key i{background:#784515;border-radius:50%;width:9px;height:9px}.power-probe{stroke:var(--fuel);fill:var(--paper);stroke-width:3px}.power-probe path{fill:none;stroke-dasharray:4 4}[data-power-cell][data-selected=true] polygon{stroke:var(--fuel);stroke-width:3px}.field-values{color:var(--muted);font-size:11px;line-height:1.8}.problem-help li{color:var(--muted);font-size:13px;line-height:1.8}.worksheet .source-locator{margin-top:35px}@media (width<=760px){.technical-figure{padding:18px}.fuel-geometry-panels{grid-template-columns:1fr;gap:28px}.fuel-geometry-panels svg{max-width:380px;margin:auto}.model-input-grid{grid-template-columns:1fr;gap:14px}.model-measure strong{font-size:34px}.model-figure .model-equation{font-size:13px}.field-readout{margin-top:5px}.investigation-table{min-width:520px}}@media (width<=420px){.fuel-geometry svg text,.fuel-geometry svg .small-label{font-size:17px}}.investigation-tool{background:var(--paper);width:100%;max-width:none;max-height:none;color:var(--ink);border:0;border-radius:0;margin:40px 0 0;padding:0;position:static;inset:auto}.investigation-tool [data-close-tool]{display:none}[data-tools-ready] .investigation-tool [data-close-tool]{display:inline-flex}.investigation-tool .tool-heading{background:var(--paper);border-bottom:1px solid var(--line);justify-content:space-between;align-items:center;gap:16px;padding:22px 28px;display:flex}.tool-heading h2{font-size:24px}.tool-heading>div{align-items:center;gap:20px;display:flex}.tool-heading button{align-items:center;gap:var(--space-xs);color:var(--ink);background:0 0;border:0;min-height:44px;padding:8px 0;font-size:13px;display:inline-flex}.tool-content{padding:28px}[data-tools-ready] .investigation-tool{overscroll-behavior:contain;border-left:1px solid var(--line);width:min(720px,100vw);max-width:100vw;height:100dvh;max-height:100dvh;margin:0;position:fixed;inset:0 0 0 auto;overflow:auto}[data-tools-ready] .investigation-tool .tool-heading{z-index:2;position:sticky;top:0}.investigation-tool::backdrop{background:#15252e55}html:has(.investigation-tool:modal){overflow:hidden}.source-records{margin:0;padding:0;list-style:none}.source-records li{border-bottom:1px solid var(--line);margin-bottom:26px;padding-bottom:26px}.source-records h3{margin-block:12px;font-size:23px;line-height:1.3}.source-records h3>a{text-underline-offset:4px;text-decoration:underline}.source-records li>p:not(.eyebrow):not(.source-locator){margin-top:18px;font-size:15px;line-height:1.8}.source-records .source-limit{color:var(--muted)}@media (width<=700px){.tool-content{padding:24px}.investigation-tool .tool-heading{padding:12px 24px}.tool-heading>div{gap:16px}.tool-heading h2{font-size:22px}}@media print{.investigation-tool,[data-tools-ready] .investigation-tool{border:0;width:100%;height:auto;max-height:none;position:static;inset:auto;overflow:visible;display:block!important}[data-tools-ready] .investigation-tool .tool-heading{position:static}.source-records li[hidden]{display:block!important}}@media screen and (prefers-reduced-motion:no-preference){main{animation:page-arrive var(--motion-quick) ease-out}@keyframes page-arrive{0%{opacity:.75}to{opacity:1}}.button{transition:background-color var(--motion-quick), border-color var(--motion-quick), color var(--motion-quick)}[data-power-cell] polygon{transition:fill var(--motion-quick), stroke var(--motion-quick)}@supports (transition-behavior:allow-discrete){[data-tools-ready] .investigation-tool[data-activated]{opacity:0;transition:opacity var(--motion-quick) var(--motion-ease), transform var(--motion-quick) var(--motion-ease), display var(--motion-quick) allow-discrete, overlay var(--motion-quick) allow-discrete;transform:translate(12px)}[data-tools-ready] .investigation-tool[data-activated][open]{opacity:1;transform:translate(0)}[data-tools-ready] .investigation-tool[data-activated]::backdrop{transition:background-color var(--motion-quick), display var(--motion-quick) allow-discrete, overlay var(--motion-quick) allow-discrete;background:0 0}[data-tools-ready] .investigation-tool[data-activated][open]::backdrop{background:#15252e55}@starting-style{[data-tools-ready] .investigation-tool[data-activated][open]{opacity:0;transform:translate(12px)}[data-tools-ready] .investigation-tool[data-activated][open]::backdrop{background:0 0}}}}.learning-conversation{padding-top:0}.conversation-opening,.conversation-body,.conversation-end,.learning-conversation>.article-connections,.learning-conversation>.article-practice{max-width:1000px;margin-inline:auto}.conversation-opening{padding-block:24px}.conversation-opening>.action-link--back{margin-bottom:12px}.conversation-opening h1{max-width:830px;font-size:clamp(34px,3.7vw,49px);line-height:1.16}.learner-question,.learner-reflection{background:var(--bubble);max-width:690px;filter:drop-shadow(var(--shadow-bubble));border-radius:20px 20px 0;margin-left:auto;padding:24px 28px;position:relative}.learner-question:after,.learner-reflection:after{content:"";border-left:20px solid #0000;border-top:14px solid var(--bubble);pointer-events:none;width:0;height:0;position:absolute;bottom:-13px;right:0}.conversation-opening .learner-question h1{font-size:clamp(28px,3vw,39px);line-height:1.2}.learner-question{margin-top:24px}.turn-label,.answer-copy>.turn-label{color:var(--muted);letter-spacing:.03em;margin:0 0 12px;font-size:12px;font-weight:600;line-height:1.4}.conversation-turn .learner-question h2{border:0;padding:0;font-size:24px}.learner-question .question-lead-in{margin:14px 0 0}.learner-question .starting-thought{margin-top:16px}.answer-copy>.answer-label{margin-bottom:12px}.starting-thought{max-width:690px;margin-top:24px;font-size:20px;line-height:1.75}.conversation-turn{scroll-margin-top:28px}.conversation-turn+.conversation-turn{margin-top:64px}.conversation-turn h2{border-left:2px solid #ad8e63;max-width:820px;padding-left:22px;font-size:29px;line-height:1.35}.question-lead-in{max-width:690px;font-size:18px;line-height:var(--leading-copy);margin-bottom:16px}.question-response{grid-template-columns:minmax(0,1fr) 205px;gap:44px;margin-top:24px;display:grid}.conversation-turn--opening-answer .question-response{margin-top:0}.answer-copy{min-width:0}.answer-copy>p{font-size:18px;line-height:var(--leading-copy)}.answer-sources{border-left:1px solid var(--line);align-self:start;padding-left:20px}.answer-sources>p{font-size:13px;font-weight:500}.answer-sources ul{margin:8px 0 0;padding:0;list-style:none}.answer-sources li+li{margin-top:8px}.answer-sources a{text-underline-offset:3px;padding-block:4px;font-size:14px;line-height:1.6;text-decoration:underline 1px;display:block}.comparison{margin-top:22px}.comparison>summary{min-height:44px;font-size:14px}.conversation-turn:has(.learner-reflection)+.conversation-turn{margin-top:28px}.learner-reflection{margin-top:32px;font-size:18px;line-height:1.75}.conversation-check{max-width:690px;margin-top:28px;padding-block:22px 0}.conversation-check .check-label{margin-bottom:16px;font-size:13px;font-weight:500}.conversation-check fieldset{border:0;margin:0;padding:0}.conversation-check .reasoning-prompt{font-size:17px;line-height:1.65}.conversation-check .answer-row{max-width:450px}.conversation-open{border-top:1px solid var(--line);max-width:690px;margin-top:48px;padding-top:26px}.conversation-open h2{font-size:25px}.conversation-open p,.conversation-open li{margin-top:18px;font-size:17px;line-height:1.8}.conversation-open ul{padding-left:22px}.more-practice{border-top:1px solid var(--line);max-width:690px;margin-top:36px}.more-practice>summary{min-height:54px;padding-block:16px;font-size:20px}.conversation-body>.practice-footer{max-width:690px}.conversation-end{border-top:1px solid var(--line);justify-content:space-between;align-items:center;gap:20px;margin-top:32px;padding-top:12px;display:flex}.conversation-end>p{color:var(--muted);font-size:12px}.conversation-end button{color:var(--accent)}@media (width<=760px){.conversation-opening{padding-block:18px 24px}.conversation-opening h1{font-size:34px}.starting-thought{margin-top:20px;font-size:18px;line-height:1.7}.conversation-turn+.conversation-turn{margin-top:44px}.conversation-turn h2{padding-left:15px;font-size:25px;line-height:1.35}.learner-question,.learner-reflection{border-radius:18px 18px 0;margin-left:16px;padding:20px}.conversation-turn .learner-question h2{padding:0;font-size:22px}.question-response{grid-template-columns:1fr;gap:20px;margin-top:20px}.answer-copy>p{font-size:17px}.answer-sources{border-left:0;padding-left:0}.answer-sources ul{flex-wrap:wrap;gap:4px 18px;margin-top:4px;display:flex}.answer-sources li+li{margin-top:0}.answer-sources a{align-items:center;min-height:44px;font-size:13px;display:flex}.learner-reflection{font-size:17px}.conversation-end{flex-direction:column;align-items:start;gap:4px}.conversation-end button{font-size:14px}}@media print{.tool-heading button{display:none}.answer-sources{border:0}.question-response{display:block}.answer-sources a{font-size:10pt}.more-practice:not([open])>:not(summary){display:block!important}.conversation-opening{padding-top:0}}.system-map{border:1px solid var(--line);border-radius:var(--radius-card);background:var(--white);padding:26px}.flow-controls{flex-wrap:wrap;gap:10px;margin-bottom:22px;display:flex}.flow-controls button{background:var(--soft);min-height:46px;color:var(--muted);border:1px solid #0000;border-radius:24px;justify-content:center;align-items:center;gap:10px;padding:10px 18px;font-size:14px;display:inline-flex}.flow-controls button[aria-pressed=true]{background:var(--white);color:var(--ink);border-color:#a3b8b0;box-shadow:0 2px 7px #182e340c}.flow-dot{border-radius:50%;width:8px;height:8px;display:inline-block}.flow-dot.material{background:var(--fuel)}.flow-dot.heat{background:var(--heat)}.flow-dot.neutrons{background:var(--neutrons)}.system-map-layout{grid-template-columns:1.6fr 1fr;align-items:center;gap:32px;display:grid}.system-map-drawing{min-width:0}.system-map-drawing svg{width:100%;height:auto;display:block}.system-map-drawing .map-small{display:none}.system-map-drawing svg text{font:16px var(--font);fill:var(--ink)}.system-map-drawing svg .map-note{fill:var(--muted);stroke:none;font-size:12px}.system-map-drawing .map-small .map-note{font-size:18px}.map-node>rect:first-child{fill:var(--paper);stroke:#a0b4b5;stroke-width:1.5px}.map-path{fill:none;stroke-width:3px;stroke-linecap:round;opacity:.5}.material-path{stroke:var(--fuel)}.heat-path{stroke:var(--heat)}.neutron-path{fill:var(--neutrons);stroke:var(--neutrons);opacity:.45}.neutron-path path{fill:none;stroke-width:2px}[data-flow=material] .material-path,[data-flow=heat] .heat-path,[data-flow=neutrons] .neutron-path{opacity:1}[data-flow=material] .fuel-node>rect:first-child,[data-flow=material] .used-node>rect:first-child{stroke:var(--fuel)}[data-flow=heat] .power-node>rect:first-child{stroke:var(--heat)}[data-flow=neutrons] .reactor-node>rect:first-child{stroke:var(--neutrons)}.system-map-drawing figcaption{color:var(--muted);max-width:600px;margin-top:20px;font-size:12px;line-height:1.75}.flow-notes>section+section{margin-top:24px}[data-map-ready] .flow-notes{display:grid}[data-map-ready] .flow-notes>section{grid-area:1/1;margin:0}.flow-notes>section[aria-hidden=true]{visibility:hidden;pointer-events:none}.flow-notes h2{font-size:29px;line-height:1.3}.flow-notes section>p:not(.map-source){margin-top:20px;font-size:17px;line-height:1.8}.flow-notes .action-link{margin-top:14px}.flow-notes .map-source{color:var(--muted);margin-top:18px;font-size:12px}.map-source a{text-underline-offset:3px;text-decoration:underline}.system-questions{margin-top:54px}.system-reading-map{grid-template-columns:1fr 1fr;gap:0 44px;display:grid}.decay-figure,.model-figure{container-type:inline-size}.decay-figure svg,.pellet-chart{overflow:visible}@container (width<=430px){.decay-figure .axis-labels text{font-size:36px}.pellet-chart .axis-labels text{font-size:34px}}.pwr-loops .loop-small text{font-size:17px}.pwr-loops .loop-small .small-label{font-size:16px}@media (prefers-reduced-motion:no-preference){.flow-controls button,.map-path,.neutron-path,.map-node>rect:first-child{transition:opacity var(--motion-quick),border-color var(--motion-quick),stroke var(--motion-quick),background-color var(--motion-quick)}.answer-feedback:not(:empty),.flow-notes section[aria-hidden=false]{animation:feedback-arrive var(--motion-quick) ease-out}@keyframes feedback-arrive{0%{opacity:.35;transform:translateY(3px)}to{opacity:1;transform:translateY(0)}}}@media (width<=1000px){.system-map-layout{grid-template-columns:1.3fr 1fr;gap:22px}.model-grid{grid-template-columns:230px minmax(0,1fr);gap:28px;padding:24px}}@media (width<=760px){:root{--space:24px}.site-header{gap:14px;min-height:72px}.site-name{margin-left:-10px}.site-name img{width:126px;height:52px}.site-header nav{gap:4px;font-size:12px}.site-header nav a{padding-inline:6px}.site-footer{margin-top:var(--space-xl);padding-block:var(--space-md);display:block}.site-footer nav{gap:4px var(--space-sm);margin-top:var(--space-xs);grid-template-columns:1fr 1fr;display:grid}.site-footer nav a{padding-inline:0}.site-footer nav a:hover,.site-footer nav a[aria-current]{color:var(--accent);background:0 0}.page-intro{padding-block:30px 28px}.page-intro h1{font-size:clamp(35px,7.5vw,48px)}.page-intro>p:last-child{margin-top:20px;font-size:17px}.section-heading{flex-wrap:wrap;gap:4px 24px;margin-bottom:16px}.section-heading h2{font-size:26px}.model-heading{display:block}.model-heading>p{max-width:none;margin-top:16px}.model-grid{grid-template-columns:1fr;gap:24px;padding:22px}.model-controls{display:block}.decay-figure{padding-inline:8px}.lesson-heading{padding-block:22px 16px}.lesson-heading h1{font-size:36px}.lesson-panel{margin-top:34px}.lesson-panel>h2,.model-heading h2{font-size:26px}.lesson-panel>p{font-size:17px}.problem-help{grid-template-columns:1fr;gap:0}.practice-footer{flex-direction:column;align-items:start;gap:4px}.print-actions{align-items:start;gap:12px;margin-bottom:28px}.print-actions .action-link--back{white-space:nowrap}.print-actions a{max-width:150px}.print-actions .button{padding:10px 13px;font-size:12px}#new-question{grid-column:1/-1;justify-self:start}dialog{padding:22px}dialog h2{font-size:28px}.system-map{border-radius:var(--radius-card);padding:20px}.system-map-layout{grid-template-columns:1fr;gap:28px}.system-map-drawing .map-wide{display:none}.system-map-drawing .map-small{max-width:390px;margin:auto;display:block}.flow-controls{gap:7px}.flow-controls button{gap:8px;padding:9px 13px;font-size:13px}.flow-notes h2{font-size:27px}.system-reading-map{grid-template-columns:1fr}.system-questions{margin-top:38px}.model-input-grid label{font-size:13px}}@media (width<=380px){:root{--space:20px}.site-name img{width:100px;height:45px}.site-header{gap:8px}.flow-controls button{padding:8px 10px}.pwr-loops{padding-inline:8px}}@media (prefers-reduced-motion:reduce){*,:before,:after{transition:none!important;animation:none!important}}@media print{@page{size:A4;margin:16mm}*,:before,:after{transition:none!important;animation:none!important}.map-path,.neutron-path{opacity:1}body{color:#111;background:#fff;font-size:11pt}.site-header,.site-footer,.skip-link,.print-actions,.no-print,.storage-warning,.flow-controls{display:none!important}.worksheet{width:100%;max-width:none;padding:0}.worksheet h1{font-size:29pt}.worksheet>p{font-size:10pt}.worksheet-problem{margin-top:22px}.worksheet-problem h2{font-size:12pt}.working-lines{background:0 0;border-bottom:1px solid #aaa;height:90px}.technical-figure,.model-grid,.system-map{background:#fff;border:1px solid #ccc}.system-map-layout,[data-map-ready] .flow-notes{display:block}.flow-notes>section[aria-hidden=true]{visibility:visible}}@media screen and (prefers-reduced-motion:no-preference){@supports (transition-behavior:allow-discrete){dialog:not(.investigation-tool){opacity:0;transition:opacity var(--motion-quick),transform var(--motion-quick) var(--motion-ease),display var(--motion-quick) allow-discrete,overlay var(--motion-quick) allow-discrete;transform:translateY(8px)}dialog:not(.investigation-tool)[open]{opacity:1;transform:translateY(0)}@starting-style{dialog:not(.investigation-tool)[open]{opacity:0;transform:translateY(8px)}}}}.field-key .power-height-key{align-items:flex-end;gap:2px;width:20px;height:19px;display:flex}.power-height-key b{background:var(--accent);width:5px;height:7px}.power-height-key b:nth-child(2){height:12px}.power-height-key b:nth-child(3){height:18px}.brand-name[data-astro-cid-mkr72gmc]{white-space:nowrap}.brand-name[data-astro-cid-mkr72gmc] strong[data-astro-cid-mkr72gmc]{font-weight:700}
