:root{color-scheme:light}.appearance{display:flex;align-items:center}.appearance select{font-size:13px;border:1px solid #d4def0;border-radius:7px;background:#f6f8ff;padding:6px 7px;color:#2542a4;min-height:36px}
.table-feature{gap:20px;padding-block:8px 16px}.table-feature>div:last-child{min-width:0}.table-feature h2{overflow-wrap:anywhere}.table-feature .feature-symbol{width:148px;height:auto;min-height:202px;padding:12px 10px;border-radius:12px;background:color-mix(in srgb,var(--tile) 32%,white);border:1px solid color-mix(in srgb,var(--ink) 18%,white)}
.feature-values{display:grid;gap:9px;width:100%;margin:0;text-align:center;line-height:1.25}.feature-values>div{margin:0}.feature-values dt{font-size:12px;font-weight:500;line-height:1.4;color:var(--ink);opacity:.9}.feature-values dd{font-size:18px;font-weight:650;line-height:1.3;margin:3px 0 0;color:var(--ink)}.feature-values .feature-chemical-symbol{display:flex;flex-direction:column-reverse}.feature-values .feature-chemical-symbol dd{font-size:46px;line-height:1;letter-spacing:-.035em;margin:0 0 3px}.feature-values .feature-atomic-weight{border-top:1px solid color-mix(in srgb,var(--ink) 16%,transparent);padding-top:8px}
html[data-theme=dark] .table-feature .feature-symbol{background:color-mix(in srgb,var(--tile) 20%,#152139);border-color:color-mix(in srgb,var(--tile) 35%,#152139)}html[data-theme=dark] .feature-values :is(dt,dd){color:color-mix(in srgb,var(--tile) 85%,white)}html[data-theme=dark] .feature-values .feature-atomic-weight{border-color:color-mix(in srgb,var(--tile) 25%,transparent)}
@media(max-width:1100px){.table-feature{gap:14px;padding-inline:10px}.table-feature .feature-symbol{width:133px}.table-feature h2{font-size:25px}.table-feature p{font-size:13px}.table-feature .eyebrow{font-size:11px}}
.hero-facts{min-width:170px;gap:12px}.hero-facts .fact dt{line-height:1.4;margin-bottom:3px}.hero-facts .fact dd{line-height:1.4}.hero-facts .hero-mass{padding-bottom:15px;border-bottom:1px solid var(--line)}.hero-facts .hero-mass dt{max-width:160px;line-height:1.5}.hero-facts .hero-mass dd{font-size:22px;color:var(--accent)}
.history-page{max-width:1000px;margin:48px auto 65px}.history-heading{border-bottom:1px solid var(--line);padding-bottom:30px;margin-bottom:35px}.history-heading h1{font-size:clamp(34px,4.3vw,58px);max-width:850px}.history-lead{font-size:20px;line-height:1.8;color:var(--muted);max-width:800px}.history-range{display:flex;align-items:center;gap:20px;font-size:13px;color:var(--accent);font-weight:600}.history-range span+span{border-inline-start:1px solid var(--line);padding-inline-start:20px}.history-timeline{list-style:none;margin:0;padding:0}.history-timeline>li{display:grid;grid-template-columns:150px minmax(0,1fr);gap:30px;position:relative;padding-bottom:30px}.history-year{padding-top:24px;font-size:23px;font-weight:650;color:var(--accent);text-align:start;white-space:nowrap}.history-event{position:relative;background:#fff;border:1px solid var(--line);border-radius:14px;padding:27px 30px}.history-event:before{content:'';position:absolute;inset-inline-start:-17px;top:33px;width:8px;height:8px;border-radius:50%;background:var(--accent)}.history-timeline>li:not(:last-child):after{content:'';position:absolute;inset-inline-start:167px;top:47px;bottom:-24px;width:1px;background:var(--line)}.history-event h2{font-size:25px;line-height:1.4;margin-bottom:12px}.history-event p{color:var(--muted);font-size:16px;line-height:1.85}.history-source{font-size:13px;color:var(--accent);text-decoration:underline;text-underline-offset:4px}.history-today{padding:30px;background:#eaf0ff;border:1px solid var(--line);border-radius:14px;margin:10px 0 35px}.history-today h2{font-size:27px}.history-today p{color:var(--muted);line-height:1.8}.history-references h2{font-size:25px}.history-references ol{padding-inline-start:22px;line-height:2.1;color:var(--accent);font-size:14px}.history-references a{text-decoration:underline;text-underline-offset:3px}.history-banner{display:block;padding:25px 30px;border:1px solid var(--line);border-inline-start:4px solid var(--accent);border-radius:12px;margin:0 0 26px;background:white}.history-banner h2{font-size:25px;margin-bottom:10px}.history-banner p{color:var(--muted)}.history-banner:hover{border-color:var(--accent)}
html[data-theme=dark] :is(.history-event,.history-banner){background:#152139}html[data-theme=dark] .history-today{background:#1d2c49}
@media(max-width:760px){.hero-facts{grid-template-columns:repeat(2,minmax(0,1fr));gap:16px 24px}.hero-facts .fact:nth-child(1){grid-column:1;grid-row:1}.hero-facts .fact:nth-child(2){grid-column:1;grid-row:2 / span 2}.hero-facts .fact:nth-child(3){grid-column:2;grid-row:1}.hero-facts .fact:nth-child(4){grid-column:2;grid-row:2}.hero-facts .fact:nth-child(5){grid-column:2;grid-row:3}.hero-facts .hero-mass{border:0;padding:0}.hero-facts .hero-mass dd{font-size:20px}.hero-facts .fact dt{font-size:13px}.history-page{margin:32px 0 45px}.history-heading h1{font-size:35px;line-height:1.4}.history-lead{font-size:17px}.history-timeline>li{grid-template-columns:minmax(0,1fr);gap:12px;padding-bottom:25px;padding-inline-start:18px}.history-year{font-size:21px;padding-top:0}.history-event{padding:22px}.history-event h2{font-size:22px}.history-event:before{display:none}.history-timeline>li:not(:last-child):after{inset-inline-start:0;top:4px;bottom:0}.history-today,.history-banner{padding:23px}.history-today h2{font-size:24px}.history-range{gap:14px}}
@media print{.history-event,.history-today{background:white!important;break-inside:avoid}.history-source,.history-banner{display:none}.history-event p,.history-year{color:#111!important}}
.header .compare-nav{display:inline-flex;align-items:center;gap:9px;min-height:40px;padding:8px 12px;border:1px solid #c6d4f5;border-radius:9px;background:#edf2ff;color:#2746b8;font-size:14px;font-weight:600;white-space:nowrap;transition:background .15s,border-color .15s}
.header .compare-nav span{display:inline}.header .compare-nav svg{width:19px;height:19px}.header .compare-nav b{display:inline-flex;align-items:center;justify-content:center;min-width:23px;height:23px;padding:0 5px;border-radius:6px;background:white;color:#425a93;font-size:12px;line-height:1}
.header .compare-nav:hover{background:#e0e9ff;border-color:#829de6}.header .compare-nav[data-selected=true] b{background:#2b4ed1;color:#fff}.header .compare-nav[aria-current=page]{border-color:#3556cc;box-shadow:0 0 0 1px #3556cc}
html[data-theme=dark] .header .compare-nav{background:#21365b;color:#dce7ff;border-color:#47618c}html[data-theme=dark] .header .compare-nav:hover{background:#2e4975;border-color:#8eabdf}html[data-theme=dark] .header .compare-nav b{background:#15243c;color:#c3d6f8}html[data-theme=dark] .header .compare-nav[data-selected=true] b{background:#a8c0ff;color:#162950}html[data-theme=dark] .header .compare-nav[aria-current=page]{border-color:#b2c8ff;box-shadow:0 0 0 1px #b2c8ff}
@media(min-width:761px) and (max-width:1150px){.header{flex-wrap:wrap}.header nav{order:3;flex-basis:100%;justify-content:center}.header-actions{margin-inline-start:auto}}
@media(max-width:760px){.header .header-actions{width:100%;justify-content:space-between;gap:8px}.header .compare-nav{font-size:13px;gap:7px;padding:7px 10px}.header .compare-nav span{display:inline}.header .compare-nav svg{width:18px;height:18px}.header .compare-nav b{height:21px;min-width:21px}}
html[data-theme=dark]{color-scheme:dark;--accent:#91afff;--navy:#e4edff;--muted:#afbdd5;--line:#2d3d58;--surface:#0d1627}
html[data-theme=dark] body{background:#0d1627;color:#e4edff}
html[data-theme=dark] :is(.header,footer,.explorer,.detail-hero,.facts-grid .fact,.aside-card.muted,.lesson-card,.production-card,.earth-banner,.contact-grid section,.compare-table){background:#152139;border-color:#2d3d58;box-shadow:none}
html[data-theme=dark] :is(h1,h2,h3,.brand,.fact dd,.element-pagination strong){color:#e4edff}
html[data-theme=dark] :is(.header nav a,.intro-sub,.intro-meta strong span,.table-feature p,.data-note,.table-meta,.legend button,.group-labels,.article-section p,.reading>p,.reading section p,.detail-heading>p:not(.eyebrow),.fact dt,.aside-card p,.lesson-card p,.page-intro p:last-child,.resource p,.world-intro p,.footer-links,.footer-note,footer p,.policy-date,.policy-heading .lead,.policy-sections p,.contact-grid p,.earth-banner p,.quiz-box p,.compare-table tbody th,.element-pagination a,.breadcrumbs,.unit-select){color:#b3c2da}
html[data-theme=dark] :is(.header nav a[aria-current],.text-link,.breadcrumbs a,.policy-bottom,.text-button,.eyebrow,#results-count,.intro-meta strong,.sources-section,.section-number){color:#a1baff}
html[data-theme=dark] :is(select,input,.search,.appearance select){background:#101c31;color:#e4edff;border-color:#3b4d6c}
html[data-theme=dark] :is(input::placeholder,.search kbd){color:#b0bfd8}
html[data-theme=dark] :is(.view-switch,.compare-nav b){background:#233451;color:#d4e2ff}
html[data-theme=dark] .view-switch button[aria-pressed=true]{background:#425a8c;color:white}
html[data-theme=dark] :is(.element,.big-element,.compare-heading){background:color-mix(in srgb,var(--tile) 22%,#152139);color:color-mix(in srgb,var(--tile) 84%,white);border-color:color-mix(in srgb,var(--tile) 28%,#152139);box-shadow:none}
html[data-theme=dark] .element:hover,html[data-theme=dark] .element:focus-visible{border-color:var(--tile);box-shadow:0 5px 22px #0008}
html[data-theme=dark] .feature-symbol{background:#253b44;color:#b9e9d0;border:1px solid #47696b;box-shadow:none}
html[data-theme=dark] :is(.note,.aside-card,.quiz-box,.formula){background:#1d2c49;color:#d4e2ff;border-color:#3b547b}
html[data-theme=dark] .learning-banner{background:#20365c;border-color:#3b547b}.learning-banner h2{color:#fff}
html[data-theme=dark] .dark{background:#466beb;color:#fff}html[data-theme=dark] .dark:hover{background:#547af7}
html[data-theme=dark] .outline{background:#152139;color:#d4e2ff;border-color:#425779}html[data-theme=dark] .outline:hover{background:#243857}
html[data-theme=dark] :is(.resource,.article-section,.policy-heading,.policy-sections section,.legend,.hero-facts,.compare-table td,.compare-table th){border-color:#2d3d58}
html[data-theme=dark] .resource:hover{background:#1d2e4c}html[data-theme=dark] .quiz-option{background:#152139;color:#d4e2ff;border-color:#4a5e7d}
html[data-theme=dark] .quiz-option.correct{background:#23483e;border-color:#78c8a1;color:#d8f7e7}html[data-theme=dark] .quiz-option.incorrect{background:#57383e;border-color:#ed9ba3;color:#ffe4e7}
html[data-theme=dark] .badge{background:#2b3e61;color:#d4e2ff}html[data-theme=dark] .bar-track{background:#293951}html[data-theme=dark] .bar-track span{background:#8daafc}
html[data-theme=dark] .series-placeholder{border-color:#536882;color:#b8c9e4}html[data-theme=dark] .series-name,html[data-theme=dark] .series-name span{color:#aebed8}
html[data-theme=dark] .toast{background:#d9e5ff;color:#162a4d}html[data-theme=dark] .brand-mark{background:#d5e2ff;color:#10264a}html[data-theme=dark] .skip{background:#1d2e4c;color:#fff}
html[data-theme=dark] :is(button,a,select,input):focus-visible{outline-color:#abc2ff}
@media(max-width:760px){.header-actions{gap:5px}.appearance select{font-size:12px;padding:5px 2px;width:76px}.header{column-gap:7px}.header .brand{font-size:18px;gap:6px}.language select{max-width:70px}}
@media print{html[data-theme=dark]{color-scheme:light}html[data-theme=dark] body{background:#fff;color:#111}html[data-theme=dark] :is(.detail-hero,.facts-grid .fact,.explorer,.compare-table){background:white;color:#111}html[data-theme=dark] :is(h1,h2,h3,p,.fact dd,.fact dt,.data-note){color:#111}html[data-theme=dark] :is(.element,.big-element){background:var(--tile);color:var(--ink)}.appearance{display:none}}

.history-heading .history-lead{font-size:19px;line-height:1.9;margin-top:24px;max-width:900px}.history-introduction{font-size:17px;line-height:1.95;color:var(--muted);max-width:900px;margin-bottom:25px}@media(max-width:760px){.history-heading .history-lead,.history-introduction{font-size:16px;line-height:1.9}}@media(min-width:1151px) and (max-width:1320px){.header{flex-wrap:wrap}.header nav{order:3;flex-basis:100%;justify-content:center}.header-actions{margin-inline-start:auto}}

/* Approved periodic-table identity: scalable mark for both languages and themes. */
.brand .site-logo-mark{width:44px;height:36px;flex-shrink:0;color:#12254d;overflow:visible}.brand{white-space:nowrap;gap:10px}html[data-theme=dark] .brand .site-logo-mark{color:#edf3ff}html[data-theme=dark] .brand .site-logo-mark g{fill:#7995ff}@media(max-width:760px){.brand .site-logo-mark{width:36px;height:30px}.brand{gap:8px}}
html.category-guide-open{overflow:hidden}.category-guide-heading{display:flex;align-items:center;justify-content:space-between;gap:16px;margin-top:26px}.category-guide-heading h2{font-size:18px;margin:0}.category-guide-heading button{border:1px solid #cbd7fb;background:#edf2ff;color:#2848e8;border-radius:10px;padding:9px 16px;font-size:14px}.category-guide{width:min(960px,94vw);max-height:89vh;max-height:89dvh;margin:auto;border:1px solid #d7e1f4;border-radius:24px;padding:0;background:#fff;color:#12254d;box-shadow:0 25px 100px #12254d30;overscroll-behavior:contain}.category-guide::backdrop{background:#12254d60;backdrop-filter:blur(3px)}.category-guide-head{padding:22px 28px 16px;background:#fff;position:sticky;top:0;border-bottom:1px solid #e4eaf5;z-index:1}.category-guide-head>div{display:flex;align-items:center;justify-content:space-between;gap:16px}.category-guide-head h2{margin:0;font-size:24px}.category-guide-head p{font-size:14px;margin:7px 0 0;color:#5c6c86}.category-guide-head button{background:#f3f6fc;color:#546581;border:1px solid #d7e1f4;border-radius:10px;font-size:25px;min-width:44px;min-height:44px}.category-guide-body{padding:20px 28px}.category-guide-note{background:#f1f5ff;border-radius:12px;padding:12px 16px;font-size:14px;margin-bottom:20px}.category-guide-grid{display:grid;grid-template-columns:1fr 1fr;gap:12px}.category-guide-card{border:1px solid #e0e7f3;border-radius:14px;padding:16px;border-inline-start:5px solid var(--category-color)}.category-guide-card h3{font-size:17px;margin:0 0 5px}.category-guide-card p{font-size:14px;line-height:1.7;color:#5c6c86;margin:0 0 10px}.category-guide-examples{color:#2848e8;font-size:13px}.category-guide-source{margin:20px 0 0;font-size:12px;color:#62718a}.category-guide-source a{color:#2848e8;text-decoration:underline}html[data-theme=dark] .category-guide,html[data-theme=dark] .category-guide-head{background:#14233c;color:#edf3ff;border-color:#344764}html[data-theme=dark] .category-guide-card{border-color:#344764;border-inline-start-color:var(--category-color)}html[data-theme=dark] .category-guide-note,html[data-theme=dark] .category-guide-heading button,html[data-theme=dark] .category-guide-head button{background:#203456;color:#dce6ff;border-color:#415a87}html[data-theme=dark] .category-guide-card p,html[data-theme=dark] .category-guide-head p,html[data-theme=dark] .category-guide-source{color:#bdcce3}html[data-theme=dark] .category-guide-examples,html[data-theme=dark] .category-guide-source a{color:#a5bdff}@media(max-width:600px){.category-guide-grid{grid-template-columns:1fr}.category-guide-body,.category-guide-head{padding:16px}.category-guide-head h2{font-size:21px}.category-guide-heading{flex-wrap:wrap}.category-guide{border-radius:18px}}
.category-actions{display:flex;flex-wrap:wrap;gap:8px}.category-click-hint{font-size:16px;color:#5b6c86;margin:8px 0 18px}.legend{gap:12px;border-top:0;padding:0;margin:0 0 20px}.legend button{gap:10px;min-height:52px;padding:10px 16px;border:1px solid #cbd6e6;background:#fff;color:#223958;border-radius:12px;font-size:17px;font-weight:650;box-shadow:0 2px 4px #12254d05;text-decoration:none}.legend button:hover{border-color:#647dd8;background:#f5f7ff;box-shadow:0 3px 10px #2848e812}.legend i{width:16px;height:16px;border-radius:5px;flex-shrink:0}.legend .category-check{width:17px;font-size:17px;color:#61708a}.legend button[aria-pressed=true]{border:2px solid #2848e8;padding:9px 15px;background:#edf2ff;color:#163bc8;box-shadow:0 0 0 3px #2848e80a;text-decoration:none}.legend button[aria-pressed=true] .category-check{color:#2848e8}.category-selection{border-top:1px solid #e3e9f2;padding-top:16px;font-size:15px;font-weight:600;color:#223958}html[data-theme=dark] .legend button{background:#172840;border-color:#52647f;color:#e1eaff}html[data-theme=dark] .legend button:hover{background:#223756;border-color:#8da6f5}html[data-theme=dark] .legend button[aria-pressed=true]{background:#253b69;border-color:#9bb3ff;color:#f1f5ff}html[data-theme=dark] .legend .category-check,html[data-theme=dark] .legend button[aria-pressed=true] .category-check{color:#adc3ff}html[data-theme=dark] .category-click-hint{color:#bdcce3}html[data-theme=dark] .category-selection{color:#dce6ff;border-color:#344764}@media(max-width:600px){.legend{gap:10px}.legend button{font-size:16px;padding:10px 12px}.legend button[aria-pressed=true]{padding:9px 11px}.category-guide-heading{align-items:flex-start}.category-click-hint{font-size:14px}}
/* Slightly more compact category controls while retaining touch-friendly height. */
.legend{gap:10px}.legend button{min-height:44px;font-size:15px;gap:8px;padding:8px 12px}.legend button[aria-pressed=true]{padding:7px 11px}.legend i{width:14px;height:14px;border-radius:4px}.legend .category-check{width:15px;font-size:15px}@media(max-width:600px){.legend{gap:8px}.legend button{font-size:14px;padding:8px 10px}.legend button[aria-pressed=true]{padding:7px 9px}}
.fact dd.physical-note{font-size:13px;font-weight:400;line-height:1.7;color:#5c6c86;margin-top:8px;overflow-wrap:anywhere}html[data-theme=dark] .fact dd.physical-note{color:#bdcce3}.physical-reference a{text-decoration:underline}.compare-table td{overflow-wrap:anywhere}