:root {
  --ink: #102440;
  --ink-soft: #52647b;
  --paper: #f6f8fb;
  --surface: #ffffff;
  --line: #dce5ef;
  --blue: #1a5d9c;
  --blue-dark: #123d6a;
  --mint: #7ee0d1;
  --gold: #f4c55f;
  --violet: #7768e7;
  --shadow: 0 18px 48px rgba(28, 56, 84, .11);
  --shadow-soft: 0 10px 26px rgba(28, 56, 84, .08);
  --radius: 22px;
  --sans: "Pretendard", "Noto Sans KR", "Apple SD Gothic Neo", system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--ink);
  background: var(--paper);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.7;
  word-break: keep-all;
}
img { max-width: 100%; }
a { color: inherit; text-decoration-thickness: 1px; text-underline-offset: 3px; }
button, input, select { font: inherit; }
button { cursor: pointer; }
:focus-visible { outline: 3px solid #efb733; outline-offset: 3px; }

.skip-link {
  position: fixed; z-index: 200; left: 12px; top: -60px; padding: 8px 14px;
  border-radius: 10px; color: #fff; background: var(--blue-dark); text-decoration: none;
}
.skip-link:focus { top: 12px; }

.shell { width: min(1180px, calc(100% - 40px)); margin: 0 auto; }
.narrow { width: min(820px, calc(100% - 40px)); margin: 0 auto; }
.section { padding: 88px 0; }
.section--tight { padding: 54px 0; }
.period-table-section { padding-top: 38px; }
.section--white { background: var(--surface); }
.section--tint { background: #eef5f9; }
.section-title { max-width: 720px; margin: 0 0 30px; }
.eyebrow { display: inline-flex; align-items: center; gap: 8px; margin: 0 0 12px; color: var(--blue); font-size: .78rem; font-weight: 800; letter-spacing: .1em; }
.eyebrow::before { width: 20px; height: 2px; background: var(--mint); content: ""; }
h1, h2, h3, p { margin-top: 0; }
h1, h2, h3 { line-height: 1.26; letter-spacing: -.045em; }
h1 { font-size: clamp(2.3rem, 5vw, 4.5rem); }
h2 { font-size: clamp(1.75rem, 3vw, 2.65rem); }
h3 { font-size: 1.16rem; }
.lead { color: var(--ink-soft); font-size: clamp(1rem, 1.5vw, 1.15rem); }
.muted { color: var(--ink-soft); }
.small { font-size: .88rem; }
.sr-only { position: absolute; width: 1px; height: 1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; }

.site-header { position: sticky; top: 0; z-index: 80; border-bottom: 1px solid rgba(220,229,239,.9); background: rgba(255,255,255,.93); backdrop-filter: blur(16px); }
.header-inner { display: flex; align-items: center; min-height: 74px; gap: 28px; }
.brand { display: inline-flex; align-items: center; gap: 10px; flex-shrink: 0; color: var(--ink); font-weight: 900; text-decoration: none; letter-spacing: -.055em; }
.brand-mark { display: grid; width: 34px; height: 34px; place-items: center; border-radius: 11px; color: #163b65; background: linear-gradient(145deg, #f6cf73, #8ae1d6); font-size: .9rem; }
.brand small { display: block; color: #668; font-size: .61rem; font-weight: 700; letter-spacing: .03em; }
.site-nav { display: flex; align-items: center; gap: 4px; margin-left: auto; }
.site-nav a { padding: 8px 10px; border-radius: 9px; color: #53657a; font-size: .91rem; font-weight: 700; text-decoration: none; white-space: nowrap; }
.site-nav a:hover, .site-nav a[aria-current="page"] { color: var(--blue-dark); background: #edf4f9; }
.nav-toggle { display: none; padding: 8px; border: 0; border-radius: 10px; color: var(--ink); background: #eef4f8; }

.hero { position: relative; overflow: hidden; padding: 90px 0 72px; background: linear-gradient(140deg, #f8fcfd 0%, #eaf2fa 58%, #f7f3e8 100%); }
.hero::before { position: absolute; width: 460px; height: 460px; right: -130px; top: -230px; border: 1px solid rgba(26,93,156,.16); border-radius: 50%; box-shadow: 0 0 0 46px rgba(126,224,209,.13), 0 0 0 93px rgba(244,197,95,.09); content: ""; }
.hero-grid { position: relative; display: grid; grid-template-columns: minmax(0, 1fr) minmax(270px, .62fr); align-items: center; gap: 56px; }
.hero h1 { max-width: 760px; margin-bottom: 20px; }
.hero h1 em { color: var(--blue); font-style: normal; }
.hero-copy { max-width: 630px; margin-bottom: 27px; color: #52677e; font-size: 1.08rem; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 11px; }
.button { display: inline-flex; min-height: 46px; align-items: center; justify-content: center; gap: 8px; padding: 10px 17px; border: 1px solid transparent; border-radius: 12px; font-weight: 800; text-decoration: none; transition: transform .18s ease, box-shadow .18s ease, background .18s ease; }
.button:hover { transform: translateY(-2px); }
.button--primary { color: #fff; background: var(--blue); box-shadow: 0 9px 18px rgba(26,93,156,.21); }
.button--primary:hover { background: var(--blue-dark); }
.button--secondary { border-color: #b9cbd8; color: var(--blue-dark); background: rgba(255,255,255,.68); }
.button--text { min-height: auto; padding: 0; color: var(--blue); background: transparent; }
.hero-trust { display: flex; flex-wrap: wrap; gap: 14px 20px; margin: 26px 0 0; padding: 0; color: #4c657f; font-size: .85rem; list-style: none; }
.hero-trust li::before { margin-right: 6px; color: #248373; content: "✓"; font-weight: 900; }

.atom-visual { position: relative; min-height: 335px; }
.atom-card { position: absolute; inset: 20px 10px 10px 15px; overflow: hidden; display: grid; place-items: center; border: 1px solid rgba(113,140,161,.2); border-radius: 34px; background: rgba(255,255,255,.68); box-shadow: var(--shadow); }
.atom-card::before, .atom-card::after { position: absolute; border: 2px solid rgba(26,93,156,.18); border-radius: 50%; content: ""; }
.atom-card::before { width: 230px; height: 112px; transform: rotate(34deg); }
.atom-card::after { width: 230px; height: 112px; transform: rotate(-34deg); }
.nucleus { position: relative; z-index: 2; display: grid; width: 91px; height: 91px; place-items: center; border-radius: 50%; color: #fff; background: radial-gradient(circle at 35% 28%, #86e4d6, #1a5d9c 65%); box-shadow: 0 8px 20px rgba(26,93,156,.3); font-size: 1.7rem; font-weight: 900; }
.electron { position: absolute; z-index: 3; width: 13px; height: 13px; border-radius: 50%; background: #f3c766; box-shadow: 0 0 0 5px rgba(243,199,102,.22); }
.electron--a { top: 72px; right: 83px; }.electron--b { bottom: 75px; left: 80px; }.electron--c { right: 42px; bottom: 145px; background: #7ee0d1; box-shadow: 0 0 0 5px rgba(126,224,209,.22); }
.atom-caption { position: absolute; right: 30px; bottom: 25px; left: 30px; z-index: 4; padding: 12px 14px; border-radius: 14px; color: #556d82; background: rgba(247,251,253,.91); font-size: .82rem; text-align: center; }

.value-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.value-card, .path-card, .info-card, .feature-card, .fact-card { border: 1px solid var(--line); border-radius: var(--radius); background: #fff; box-shadow: var(--shadow-soft); }
.value-card { padding: 27px; }
.value-number { display: block; margin-bottom: 9px; color: var(--blue); font-size: 1.65rem; font-weight: 900; letter-spacing: -.06em; }
.value-card p { margin-bottom: 0; color: var(--ink-soft); font-size: .93rem; }

.tool-intro { display: flex; align-items: end; justify-content: space-between; gap: 28px; margin-bottom: 24px; }
.period-table-section .tool-intro { margin-bottom: 16px; }
.period-table-section .tool-intro h1 { margin: 0; font-size: clamp(2rem, 3.3vw, 3rem); }
.tool-intro .section-title { margin-bottom: 0; }
.data-status { flex: 0 0 auto; padding: 11px 13px; border: 1px solid #d3e5db; border-radius: 12px; color: #2f7163; background: #f1fbf7; font-size: .8rem; font-weight: 750; }
.table-tool { border: 1px solid #d7e2ea; border-radius: 26px; background: #fff; box-shadow: var(--shadow); }
.tool-controls { padding: 22px; border-bottom: 1px solid var(--line); }
.search-wrap { position: relative; }
.search-wrap svg { position: absolute; top: 50%; left: 15px; width: 18px; transform: translateY(-50%); color: #72849a; pointer-events: none; }
.search-wrap input { width: 100%; min-height: 51px; padding: 12px 16px 12px 47px; border: 1px solid #cfdde8; border-radius: 13px; color: var(--ink); background: #fbfdff; }
.search-wrap input::placeholder { color: #8798aa; }
.filter-row { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 13px; }
.filter-row--secondary { margin-top: 8px; padding-top: 10px; border-top: 1px solid #e0e8ee; }.filter-row--secondary > span { align-self: center; margin-right: 2px; color: #6b8194; font-size: .75rem; font-weight: 800; }
.filter-button { padding: 7px 10px; border: 1px solid #d6e1e9; border-radius: 999px; color: #4e657c; background: #fff; font-size: .79rem; font-weight: 750; }
.filter-button:hover, .filter-button.is-active { border-color: #a7c7db; color: #124b79; background: #eaf5fa; }
.hover-note { position: fixed; z-index: 120; display: none; width: min(310px, calc(100vw - 28px)); padding: 11px 13px; border: 1px solid #9db4c5; border-radius: 8px; color: #28445f; background: #fff; box-shadow: 0 8px 22px rgba(34, 63, 89, .15); font-size: .82rem; line-height: 1.55; pointer-events: none; }
.hover-note.is-visible { display: block; }
.result-meta { margin: 13px 0 0; color: #60758b; font-size: .83rem; }
.periodic-stage { border-top: 1px solid #e0e8ee; }.periodic-wrap { overflow-x: hidden; padding: 21px 22px 25px; }
.trend-controls { display: flex; align-items: center; gap: 8px; padding: 14px 22px; border-bottom: 1px solid #e0e8ee; background: #fbfdfe; }.trend-controls > p { margin: 0 4px 0 0; color: #61798e; font-size: .74rem; font-weight: 850; white-space: nowrap; }.trend-controls > button { padding: 7px 10px; border: 1px solid #d6e2ea; border-radius: 7px; color: #365976; background: #fff; text-align: left; }.trend-controls > button:hover, .trend-controls > button.is-active { border-color: #7a9ab5; background: #f1f8fb; }.trend-controls > button b, .trend-controls > button span { display: block; }.trend-controls > button b { font-size: .78rem; }.trend-controls > button span { margin-top: 2px; color: #6b8194; font-size: .68rem; }.trend-panel { margin: 0 22px; padding: 12px 0; border-bottom: 1px solid #dce6ed; }.trend-panel h3 { margin: 0 0 8px; color: #244f75; font-size: .8rem; }.trend-panel p { display: grid; grid-template-columns: 18px 1fr; gap: 4px; margin: 0 0 8px; color: #587187; font-size: .7rem; line-height: 1.35; }.trend-panel p b { grid-row: span 2; color: #1d5b8d; font-size: 1rem; }.trend-panel p span { color: #60798d; }.trend-panel p strong { color: #294d6c; font-size: .7rem; }.trend-panel small { display: block; color: #708595; font-size: .68rem; line-height: 1.42; }
.periodic-grid { display: grid; grid-template-columns: 34px repeat(18, minmax(0, 1fr)); grid-template-rows: 30px repeat(7, 70px); width: 100%; min-width: 0; gap: 5px; }.periodic-grid.is-series-open { grid-template-rows: 30px repeat(9, 70px); }
.periodic-axis { display: grid; place-items: center; color: #58728a; font-size: .76rem; font-weight: 850; font-variant-numeric: tabular-nums; line-height: 1.15; text-align: center; }.periodic-axis--corner { color: #3f5f7c; font-size: .67rem; white-space: pre-line; }.periodic-axis--group { border-bottom: 1px solid #d7e2e9; }.periodic-axis--period { border-right: 1px solid #d7e2e9; }
.element { position: relative; overflow: hidden; display: flex; flex-direction: column; align-items: flex-start; justify-content: center; min-width: 0; padding: 8px 8px 7px; border: 1px solid transparent; border-radius: 10px; color: #183654; text-align: left; transition: transform .15s ease, box-shadow .15s ease, opacity .15s ease; }
.element:hover { z-index: 3; transform: translateY(-2px) scale(1.04); border-color: rgba(24,54,84,.25); box-shadow: 0 7px 15px rgba(30,66,98,.16); }
.element:focus-visible { z-index: 4; }
.element.is-muted { opacity: .16; }.element.is-series-hidden { display: none; }
.element.is-selected { z-index: 4; border: 2px solid var(--blue-dark); box-shadow: 0 0 0 3px rgba(26,93,156,.16); }
.element-number { color: #52718d; font-size: .66rem; font-variant-numeric: tabular-nums; line-height: 1; }
.element-symbol { margin: 4px 0 0; font-size: 1.4rem; font-weight: 900; letter-spacing: -.05em; line-height: 1; }
.element-name { display: block; overflow: hidden; max-width: 100%; margin-top: 5px; color: #385a75; font-size: .66rem; font-weight: 800; line-height: 1.12; letter-spacing: -.055em; white-space: nowrap; text-overflow: clip; }
.element--metal { background: #fce2b8; }.element--metalloid { background: #e6dcfa; }.element--nonmetal { background: #cbeee3; }.element--unknown { background: #e8edf1; }
.series-toggle { display: grid; align-content: center; justify-items: center; min-width: 0; padding: 5px 3px; border: 1px dashed #9eb5c7; border-radius: 6px; color: #3e617d; background: #f5f9fb; font: inherit; text-align: center; line-height: 1.2; cursor: pointer; }
.series-toggle span { font-size: .62rem; font-weight: 800; }
.series-toggle strong { margin-top: 3px; font-size: .66rem; letter-spacing: -.04em; }
.series-toggle:hover, .series-toggle:focus-visible { border-style: solid; border-color: #6289a7; background: #eaf4f8; outline: none; }
.legend { display: flex; flex-wrap: wrap; gap: 8px 13px; margin: 18px 0 0; padding: 0; list-style: none; color: #60758b; font-size: .73rem; }
.legend i { display: inline-block; width: 10px; height: 10px; margin-right: 4px; border-radius: 3px; vertical-align: -1px; }

.detail-panel { margin: 0 22px 22px; border: 1px solid #cce0ec; border-radius: 19px; background: linear-gradient(120deg, #f4fbfc, #f8f7ff); }
.detail-panel[hidden] { display: none; }
.detail-top { display: grid; grid-template-columns: auto minmax(0, 1fr) auto; gap: 19px; align-items: start; padding: 23px 23px 0; }
.detail-token { display: grid; width: 75px; height: 75px; place-items: center; border-radius: 18px; background: #daf0ee; color: #173e68; }
.detail-token b { font-size: 1.85rem; letter-spacing: -.08em; line-height: 1; }.detail-token span { font-size: .68rem; }
.detail-heading h3 { margin: 0 0 2px; font-size: 1.56rem; }.detail-heading p { margin: 0; color: #536d84; font-size: .91rem; }
.detail-close { width: 36px; height: 36px; border: 0; border-radius: 10px; color: #426078; background: #e7f0f5; font-size: 1.22rem; }
.detail-body { display: grid; grid-template-columns: minmax(280px, .92fr) minmax(0, 1.35fr); gap: 18px; padding: 21px 23px 23px; }
.detail-sidebar { min-width: 0; }
.detail-copy { color: #3b556e; }.detail-copy p:last-child { margin-bottom: 0; }
.detail-facts { display: grid; grid-template-columns: repeat(2, 1fr); gap: 9px; margin: 0; }
.detail-facts div { padding: 10px 11px; border-radius: 12px; background: rgba(255,255,255,.78); }.detail-facts dt { color: #648097; font-size: .69rem; font-weight: 750; }.detail-facts dd { margin: 2px 0 0; color: #163d67; font-size: .89rem; font-weight: 900; }
.detail-facts .detail-fact--wide { grid-column: 1 / -1; }.detail-facts .detail-fact--muted { color: #718294; }.detail-facts .detail-fact--muted dd { color: #718294; font-weight: 750; }.electron-configuration { font-family: ui-monospace, SFMono-Regular, Consolas, "Liberation Mono", monospace; font-size: .82rem !important; letter-spacing: -.02em; overflow-wrap: anywhere; }
.material-brief { margin-top: 10px; padding: 12px; border: 1px solid #d9e4ec; border-radius: 8px; color: #48657b; background: #fff; }.material-brief > b { display: block; color: #59758b; font-size: .7rem; }.material-brief p { margin: 4px 0 3px; color: #19486f; font-size: .9rem; font-weight: 850; }.material-brief p span { color: #667f92; font-size: .78rem; }.material-brief small { display: block; color: #5d7387; font-size: .76rem; line-height: 1.42; }
.term-label { padding: 0; border: 0; color: inherit; background: transparent; font: inherit; text-decoration: underline dotted; text-underline-offset: 3px; cursor: help; }

.path-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 18px; }
.path-card { padding: 27px; }.path-step { display: inline-grid; width: 30px; height: 30px; place-items: center; margin-bottom: 16px; border-radius: 50%; color: #fff; background: var(--blue); font-size: .79rem; font-weight: 900; }.path-card p { color: var(--ink-soft); font-size: .91rem; }.path-links { display: flex; flex-wrap: wrap; gap: 7px; }.concept-link { border: 0; padding: 0; color: var(--blue); background: none; font-weight: 800; text-decoration: underline; text-decoration-thickness: 1px; text-underline-offset: 3px; }

.glossary-layout { display: grid; grid-template-columns: minmax(0, 1fr) 320px; gap: 36px; align-items: start; }
.glossary-list { display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px; }
.glossary-pagination { display: flex; gap: 6px; margin-top: 18px; }.glossary-pagination button { display: grid; width: 34px; height: 34px; place-items: center; border: 1px solid #cad8e3; border-radius: 7px; color: #41607b; background: #fff; font-size: .84rem; font-weight: 800; }.glossary-pagination button.is-active { border-color: #2b5b85; color: #fff; background: #2b5b85; }
.glossary-item { width: 100%; min-height: 119px; padding: 17px; border: 1px solid var(--line); border-radius: 17px; color: var(--ink); background: #fff; text-align: left; transition: transform .16s ease, box-shadow .16s ease; }.glossary-item:hover { transform: translateY(-2px); box-shadow: var(--shadow-soft); }.glossary-item.is-active { border-color: #8dbbd6; background: #f3fbff; }.glossary-item strong { display: block; font-size: 1rem; }.glossary-item small { color: #658096; }.glossary-item span { display: block; margin-top: 7px; color: #566d82; font-size: .82rem; line-height: 1.5; }
.glossary-detail { position: sticky; top: 95px; padding: 24px; border: 1px solid #c8dbe7; border-radius: 21px; background: #f3fafc; }.glossary-detail .level { display: inline-block; margin-bottom: 9px; padding: 3px 8px; border-radius: 999px; color: #156052; background: #d9f3eb; font-size: .7rem; font-weight: 850; }.glossary-detail h3 { margin-bottom: 5px; }.glossary-detail p { color: #506b82; font-size: .9rem; }.glossary-next { margin: 15px 0 0; padding: 14px; border-radius: 14px; background: #fff; }.glossary-next b { display: block; margin-bottom: 7px; font-size: .78rem; }.glossary-next button { margin: 2px; padding: 5px 8px; border: 1px solid #d2e0ea; border-radius: 999px; color: #184c79; background: #f8fbfd; font-size: .75rem; font-weight: 800; }
.glossary-expanded { margin: 16px 0; padding: 13px 0 0; border-top: 1px solid #cfdee7; }.glossary-expanded summary { cursor: pointer; color: #234f75; font-size: .84rem; font-weight: 850; }.glossary-expanded p { margin: 12px 0; }.glossary-expanded b { display: block; margin-top: 14px; color: #355c7e; font-size: .8rem; }.glossary-expanded ul { margin: 7px 0 0; padding-left: 18px; color: #506b82; font-size: .83rem; line-height: 1.55; }

.callout { padding: 28px; border-radius: 24px; color: #e5f3fb; background: linear-gradient(120deg, #163d67, #1d628c); }.callout h2 { margin-bottom: 11px; color: #fff; }.callout p { max-width: 800px; margin-bottom: 0; color: #c6e0ef; }.callout-grid { display: grid; grid-template-columns: 1fr auto; gap: 32px; align-items: center; }
.faq { display: grid; gap: 10px; }.faq details { padding: 0 20px; border: 1px solid var(--line); border-radius: 15px; background: #fff; }.faq summary { padding: 17px 0; cursor: pointer; font-weight: 850; }.faq p { color: var(--ink-soft); font-size: .92rem; }

.article-hero { padding: 72px 0 50px; background: linear-gradient(130deg, #edf7f8, #f6f2e9); }.article-hero .lead { max-width: 760px; }.article { padding: 67px 0 88px; background: #fff; }.article h2 { margin-top: 50px; }.article h2:first-child { margin-top: 0; }.article h3 { margin-top: 28px; }.article p, .article li { color: #465e75; }.article li + li { margin-top: 7px; }.article a { color: var(--blue); }.article a.button--primary { color: #fff; }.article-note { margin: 25px 0; padding: 18px 20px; border-left: 4px solid #62bda9; border-radius: 0 15px 15px 0; background: #f1faf7; color: #42675f; }.article-table { width: 100%; border-collapse: collapse; margin: 23px 0; border: 1px solid var(--line); border-radius: 14px; overflow: hidden; font-size: .93rem; }.article-table th, .article-table td { padding: 12px 14px; border-bottom: 1px solid var(--line); text-align: left; }.article-table th { color: #2d5475; background: #f1f7fa; }.article-table tr:last-child td { border-bottom: 0; }
.concept-page { min-height: 72vh; }.concept-page .lead { max-width: 680px; }.concept-longform { max-width: 720px; margin-top: 34px; }.concept-longform p { color: #445e76; font-size: 1.04rem; }.concept-page h2 { margin-top: 44px; font-size: 1.5rem; }.concept-page li { color: #445e76; }.concept-page-links { display: flex; flex-wrap: wrap; gap: 8px; }

.footer { padding: 48px 0 32px; border-top: 1px solid #d9e3eb; color: #536b80; background: #f6f8fb; }.footer-grid { display: grid; grid-template-columns: 1.4fr repeat(3, 1fr); gap: 25px; }.footer h2 { margin-bottom: 8px; font-size: 1.08rem; }.footer p, .footer li { font-size: .84rem; }.footer ul { margin: 0; padding: 0; list-style: none; }.footer li + li { margin-top: 7px; }.footer a { text-decoration: none; }.footer a:hover { color: var(--blue); text-decoration: underline; }.footer-bottom { display: flex; justify-content: space-between; gap: 18px; margin-top: 34px; padding-top: 20px; border-top: 1px solid #d9e3eb; font-size: .77rem; }

@media (max-width: 900px) {
  .header-inner { gap: 12px; }.nav-toggle { display: inline-flex; margin-left: auto; }.site-nav { position: absolute; top: 73px; right: 18px; left: 18px; display: none; flex-direction: column; align-items: stretch; padding: 9px; border: 1px solid #dae5ec; border-radius: 14px; background: #fff; box-shadow: var(--shadow); }.site-nav.is-open { display: flex; }.site-nav a { padding: 11px; }.hero { padding-top: 62px; }.hero-grid, .glossary-layout { grid-template-columns: 1fr; }.atom-visual { width: min(420px, 100%); margin: 0 auto; }.value-grid, .path-grid { grid-template-columns: 1fr; }.tool-intro { display: block; }.data-status { display: inline-block; margin-top: 14px; }.detail-body { grid-template-columns: 1fr; }.glossary-detail { position: static; order: -1; }.footer-grid { grid-template-columns: repeat(2, 1fr); }
}
@media (max-width: 600px) {
  body { font-size: 15px; }.shell, .narrow { width: min(100% - 28px, 1180px); }.section { padding: 58px 0; }.hero { padding: 55px 0 52px; }.hero h1 { font-size: 2.25rem; }.atom-visual { min-height: 280px; }.atom-card { inset: 12px 3px 5px; }.atom-card::before, .atom-card::after { width: 190px; height: 92px; }.nucleus { width: 76px; height: 76px; }.electron--a { top: 54px; right: 54px; }.electron--b { bottom: 55px; left: 55px; }.electron--c { right: 22px; bottom: 118px; }.tool-controls, .periodic-wrap { padding: 15px; }.trend-controls { display: grid; grid-template-columns: auto repeat(2, minmax(0, 1fr)); gap: 7px; padding: 14px 15px; }.trend-controls > p { align-self: center; margin: 0; }.trend-panel { margin: 0 15px; }.detail-panel { margin: 0 15px 15px; }.detail-top, .detail-body { padding-right: 16px; padding-left: 16px; }.detail-top { grid-template-columns: auto 1fr; }.detail-close { grid-column: 2; justify-self: end; margin-top: -44px; }.detail-token { width: 64px; height: 64px; }.detail-facts { grid-template-columns: 1fr 1fr; }.glossary-list { grid-template-columns: 1fr; }.callout-grid { grid-template-columns: 1fr; }.footer-grid { grid-template-columns: 1fr 1fr; gap: 20px; }.footer-grid > :first-child { grid-column: 1 / -1; }.footer-bottom { display: block; }.footer-bottom p + p { margin-top: 8px; }
}

/* Calm learning-tool visual reset: information first, decoration second. */
:root {
  --paper: #f8fafc;
  --surface: #ffffff;
  --line: #d9e2ec;
  --blue: #245b8f;
  --blue-dark: #1b456e;
  --mint: #a8d8cf;
  --gold: #e8d39a;
  --shadow: none;
  --shadow-soft: none;
  --radius: 14px;
}
body { background: var(--paper); }
.site-header { background: #fff; backdrop-filter: none; }
.brand-mark { border-radius: 8px; background: #e7f1f5; color: var(--blue-dark); }
.site-nav a { border-radius: 7px; }
.hero { padding: 76px 0 62px; background: #f1f5f8; }
.hero::before { display: none; }
.hero-grid { grid-template-columns: minmax(0, 1fr) 255px; gap: 42px; }
.hero h1 { max-width: 800px; font-size: clamp(2.25rem, 4.5vw, 3.8rem); }
.hero h1 em { color: var(--blue-dark); }
.hero-copy { max-width: 600px; color: #526779; }
.button { min-height: 43px; border-radius: 8px; box-shadow: none; }
.button:hover { transform: none; }
.button--primary { background: var(--blue-dark); }
.button--primary:hover { background: #153956; }
.button--secondary { border-color: #bdcad6; background: #fff; }
.atom-visual { min-height: 205px; }
.atom-card { inset: 0; display: grid; grid-template-columns: 84px 1fr; place-items: center; gap: 20px; padding: 28px; border: 1px solid #ccd9e4; border-radius: 14px; background: #fff; box-shadow: none; }
.atom-card::before, .atom-card::after, .electron { display: none; }
.nucleus { width: 72px; height: 72px; border: 1px solid #7c9eb7; border-radius: 10px; color: var(--blue-dark); background: #e9f3f5; box-shadow: none; font-size: 1.55rem; }
.atom-caption { position: static; width: auto; padding: 0; border-radius: 0; color: #50687d; background: transparent; font-size: .84rem; text-align: left; line-height: 1.6; }
.atom-caption strong { color: var(--blue-dark); }
.value-card, .path-card, .info-card, .feature-card, .fact-card, .table-tool { border-radius: 14px; box-shadow: none; }
.value-card { padding: 24px; }
.value-number { color: var(--blue-dark); font-size: 1rem; letter-spacing: 0; }
.section--tint { background: #f1f5f8; }
.data-status { border-color: #c9dde0; border-radius: 8px; color: #356c66; background: #f4fbfa; }
.tool-controls { padding: 19px; }
.search-wrap input { min-height: 48px; border-radius: 8px; background: #fff; }
.filter-button { border-radius: 7px; }
.periodic-wrap { padding: 19px; }
.periodic-grid { gap: 4px; }
.element { border-radius: 6px; }
.element:hover { transform: none; border-color: #65839e; box-shadow: none; }
.element.is-selected { border: 2px solid var(--blue-dark); box-shadow: none; }
.series-toggle { border-radius: 6px; }
.detail-panel { border-radius: 12px; background: #f5f9fb; }
.detail-top { padding-top: 20px; }
.detail-token { border-radius: 10px; }
.detail-close { border-radius: 7px; }
.detail-facts div { border: 1px solid #e0e8ee; border-radius: 8px; background: #fff; }
.study-route { border-radius: 10px; background: #254e75; }
.study-route-links button { border-radius: 6px; }
.glossary-item { min-height: 109px; border-radius: 10px; box-shadow: none; }
.glossary-item:hover { transform: none; box-shadow: none; border-color: #9db4c5; }

/* On ordinary screens the grid fits its container. Narrow screens keep the
   readable cells but use swipe scrolling without a persistent scrollbar. */
@media (max-width: 820px) {
  .periodic-wrap { overflow-x: auto; -ms-overflow-style: none; scrollbar-width: none; }
  .periodic-wrap::-webkit-scrollbar { display: none; }
  .periodic-grid { grid-template-columns: 30px repeat(18, minmax(52px, 1fr)); min-width: 970px; }
}
.glossary-detail { border-radius: 12px; background: #f4f8fa; }
.glossary-next { border: 1px solid #e0e8ee; border-radius: 8px; }
.path-step { border-radius: 7px; background: #ddebf2; color: var(--blue-dark); }
.callout { border: 1px solid #bdd0df; border-radius: 14px; background: #edf5f8; color: var(--ink); }
.callout h2 { color: var(--blue-dark); }
.callout p { color: #50687c; }
.faq details { border-radius: 10px; }
.article-hero { padding: 64px 0 46px; background: #f1f5f8; }
.article { padding-top: 58px; }
.article-note { border-left-color: #6aa698; border-radius: 0 8px 8px 0; background: #f3faf7; }
.article-table { border-radius: 10px; }
.footer { background: #f1f5f8; }

@media (max-width: 900px) {
  .hero-grid { grid-template-columns: 1fr; gap: 24px; }
  .atom-visual { width: 100%; max-width: none; min-height: auto; margin: 0; }
}
@media (max-width: 600px) {
  .hero { padding: 56px 0 48px; }
  .hero h1 { font-size: 2.15rem; }
  .atom-card { grid-template-columns: 64px 1fr; gap: 15px; padding: 18px; }
  .nucleus { width: 58px; height: 58px; font-size: 1.3rem; }
}

/* Element exploration upgrades: keep the visual layer quiet and the data first. */
.quick-elements { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; margin-top: 11px; }
.quick-elements > span { margin-right: 3px; color: #6b8194; font-size: .72rem; font-weight: 800; }
.quick-elements button { padding: 4px 7px; border: 1px solid #dce6ec; border-radius: 6px; color: #466780; background: #fff; font-size: .71rem; font-weight: 750; }
.quick-elements button:hover, .quick-elements button:focus-visible { border-color: #84a6bd; color: #173e68; background: #eef7fa; outline: none; }
.filter-note { margin: 11px 0 0; padding: 9px 11px; border-left: 3px solid #84aabd; color: #4d687e; background: #f5fafc; font-size: .78rem; line-height: 1.5; }

.detail-actions { display: flex; align-items: center; gap: 8px; }
.compare-toggle, .compare-clear { padding: 8px 10px; border: 1px solid #a9c0d1; border-radius: 7px; color: #1d517b; background: #fff; font-size: .76rem; font-weight: 800; white-space: nowrap; }
.compare-toggle[aria-pressed="true"] { border-color: #547d9a; color: #fff; background: #315f84; }
.element-overview { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 9px; margin: 17px 22px 0; }
.overview-card { min-width: 0; padding: 12px; border: 1px solid #dce7ed; border-radius: 8px; background: #fff; }
.overview-card > span { display: block; color: #668197; font-size: .68rem; font-weight: 800; }
.overview-card strong { display: block; margin-top: 4px; color: #204c74; font-size: .9rem; line-height: 1.35; }
.overview-card p { margin: 4px 0 0; color: #60788c; font-size: .74rem; line-height: 1.45; }
.orbital-map { padding: 16px; border: 1px solid #d5e2ea; border-radius: 9px; background: #fff; }.orbital-map-head { display: flex; align-items: center; justify-content: space-between; gap: 8px; color: #234e76; }.orbital-map-head > b { font-size: .88rem; }.orbital-map-head > span { color: #6c8191; font-size: .69rem; }.orbital-intro { margin: 9px 0 0; color: #637b8e; font-size: .74rem; line-height: 1.45; }.orbital-legend { display: flex; gap: 5px; margin: 11px 0; }.orbital-key { display: grid; width: 23px; height: 23px; place-items: center; border: 1px solid currentColor; color: #657d8f; font-size: .77rem; font-weight: 900; }.orbital-key--s, .orbital-row--s .orbital-box { color: #a55470; background: #fde5ec; }.orbital-key--p, .orbital-row--p .orbital-box { color: #217f6b; background: #def7ef; }.orbital-key--d, .orbital-row--d .orbital-box { color: #6f7e21; background: #eef8c8; }.orbital-key--f, .orbital-row--f .orbital-box { color: #526caa; background: #e3eafd; }.orbital-rows { display: grid; gap: 6px; }.orbital-row { display: grid; grid-template-columns: 30px minmax(0, 1fr) 43px; align-items: center; gap: 7px; }.orbital-row > b { color: #45647a; font-size: .78rem; text-align: right; }.orbital-row > span { color: #5f788b; font-size: .7rem; white-space: nowrap; }.orbital-boxes { display: flex; gap: 4px; min-width: 0; }.orbital-box { display: grid; grid-template-columns: 1fr 1fr; width: 38px; height: 34px; place-items: center; border: 1px solid currentColor; font-style: normal; font-size: 1.15rem; font-weight: 900; line-height: 1; }.orbital-arrow { display: grid; width: 100%; height: 100%; place-items: center; font-family: Arial, sans-serif; }.orbital-arrow--down { border-left: 1px solid currentColor; }.orbital-shells { margin: 13px 0 0; padding-top: 11px; border-top: 1px solid #e0e9ef; color: #597286; font-size: .76rem; }.orbital-shells b { color: #244f76; letter-spacing: .08em; }.orbital-map--unavailable p { margin: 11px 0 0; color: #667e90; font-size: .8rem; line-height: 1.5; }
.detail-characteristic { margin-top: 12px; padding: 15px 16px; border-left: 3px solid #82a9ba; color: #405c73; background: #edf5f8; }.detail-characteristic > span { display: block; color: #51738d; font-size: .7rem; font-weight: 850; }.detail-characteristic p { margin: 6px 0 0; line-height: 1.65; }.detail-reference { margin-top: 12px; color: #62798c; font-size: .77rem; }.detail-reference summary { cursor: pointer; color: #456780; font-weight: 800; }.detail-reference p { margin: 8px 0 0; line-height: 1.5; }

.compare-panel { margin: 0 22px 22px; padding: 18px; border: 1px solid #cbdce7; border-radius: 10px; background: #f9fcfd; }.compare-panel[hidden] { display: none; }.compare-heading { display: flex; justify-content: space-between; gap: 16px; align-items: start; }.compare-heading > div > span { color: #55788f; font-size: .7rem; font-weight: 850; }.compare-heading h3 { margin: 3px 0 0; color: #1e4c75; font-size: 1.04rem; }.compare-heading p { margin: 5px 0 0; color: #61798c; font-size: .79rem; line-height: 1.45; }.compare-cards { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 12px; margin-top: 15px; }.compare-card { min-width: 0; padding: 13px; border: 1px solid #dbe6ec; border-radius: 8px; background: #fff; }.compare-card header { display: grid; grid-template-columns: 38px minmax(0, 1fr) auto; align-items: center; gap: 9px; padding-bottom: 11px; border-bottom: 1px solid #e4ecf1; }.compare-symbol { display: grid; width: 38px; height: 38px; place-items: center; border-radius: 7px; color: #1f4c74; font-size: 1.1rem; font-weight: 900; }.compare-card header b, .compare-card header span { display: block; }.compare-card header b { color: #214d75; font-size: .9rem; }.compare-card header div > span { margin-top: 1px; color: #718595; font-size: .7rem; }.compare-card header button { width: 26px; height: 26px; border: 0; border-radius: 5px; color: #587388; background: #edf3f6; font-size: 1.05rem; }.compare-card dl { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; margin: 11px 0 0; }.compare-card dl div { min-width: 0; }.compare-card dt { color: #718698; font-size: .66rem; }.compare-card dd { margin: 2px 0 0; color: #34556f; font-size: .75rem; font-weight: 750; line-height: 1.42; overflow-wrap: anywhere; }

/* Relationship explorer: two chosen elements stay central; explanations remain secondary. */
.comparison-picker { display: grid; grid-template-columns: minmax(0, 1fr) auto minmax(0, 1fr) auto; align-items: end; gap: 9px; margin-top: 17px; padding: 13px; border: 1px solid #dbe6ec; border-radius: 8px; background: #fff; }.comparison-picker > div { min-width: 0; }.comparison-picker label { display: block; margin-bottom: 5px; color: #617c91; font-size: .69rem; font-weight: 800; }.comparison-picker input { width: 100%; min-height: 38px; box-sizing: border-box; padding: 0 9px; border: 1px solid #cbdbe5; border-radius: 6px; color: #244d72; background: #fff; font: inherit; font-size: .82rem; }.comparison-picker input:focus { border-color: #7198b6; outline: 2px solid rgba(87, 138, 177, .16); outline-offset: 1px; }.comparison-picker > span { padding-bottom: 9px; color: #6a859a; font-weight: 850; }.comparison-picker button, .relationship-save { min-height: 38px; padding: 0 11px; border: 1px solid #2e658d; border-radius: 6px; color: #fff; background: #2e658d; font: inherit; font-size: .78rem; font-weight: 850; white-space: nowrap; }.comparison-picker button:hover, .relationship-save:hover { background: #1f537a; }.comparison-picker-help { grid-column: 1 / -1; margin: 1px 0 0; color: #6e8494; font-size: .69rem; }.comparison-tabs { display: flex; gap: 5px; margin-top: 15px; border-bottom: 1px solid #dbe6ec; }.comparison-tabs button { padding: 8px 10px; border: 0; border-bottom: 2px solid transparent; color: #6a8192; background: transparent; font: inherit; font-size: .77rem; font-weight: 850; }.comparison-tabs button.is-active { border-bottom-color: #2d658d; color: #1f5178; }.relationship-view { margin-top: 15px; }.relationship-title { display: flex; justify-content: space-between; gap: 14px; align-items: start; margin-bottom: 14px; }.relationship-title > div > span, .relationship-insights span, .relationship-facts > h4, .relationship-concepts > b { color: #597b94; font-size: .7rem; font-weight: 850; }.relationship-title h3 { margin: 4px 0 0; color: #204e76; font-size: 1rem; }.relationship-title p { margin: 5px 0 0; color: #60798e; font-size: .78rem; }.relationship-save[aria-pressed="true"] { border-color: #809aad; color: #315d7e; background: #edf5f9; }.relationship-facts { padding-top: 14px; border-top: 1px solid #dfe9ef; }.relationship-facts > h4 { margin: 0 0 9px; }.relationship-facts-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 11px; }.relationship-facts-card { min-width: 0; padding: 12px; border: 1px solid #dbe6ec; border-radius: 8px; background: #fff; }.relationship-facts-card header { display: grid; grid-template-columns: 38px minmax(0, 1fr); align-items: center; gap: 9px; padding-bottom: 10px; border-bottom: 1px solid #e4edf1; }.relationship-facts-card header b, .relationship-facts-card header span { display: block; }.relationship-facts-card header b { color: #214d75; font-size: .88rem; }.relationship-facts-card header span { color: #718595; font-size: .7rem; }.relationship-facts-card dl { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; margin: 11px 0 0; }.relationship-facts-card dl div { min-width: 0; }.relationship-facts-card dt { color: #718698; font-size: .65rem; }.relationship-facts-card dd { margin: 2px 0 0; color: #34556f; font-size: .74rem; font-weight: 750; line-height: 1.42; overflow-wrap: anywhere; }.relationship-facts-card .relationship-fact--wide { grid-column: 1 / -1; }.relationship-insights { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 10px; margin-top: 12px; }.relationship-insights article { min-width: 0; padding: 12px; border: 1px solid #dbe6ec; border-radius: 8px; background: #fff; }.relationship-insights ul { margin: 7px 0 0; padding-left: 17px; color: #435f75; font-size: .78rem; line-height: 1.55; }.relationship-insights li + li { margin-top: 5px; }.relationship-insights p { margin: 7px 0 0; color: #526c82; font-size: .78rem; line-height: 1.55; }.relationship-insights .relationship-reason { background: #f2f8fa; }.relationship-insights .relationship-caution { border-color: #d9d9c6; background: #fbfaf3; }.relationship-insights .relationship-caution > span { color: #7b7554; }.relationship-concepts { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; margin-top: 13px; }.relationship-concepts > b { margin-right: 3px; }.relationship-concepts button, .confusable-concepts button { padding: 5px 7px; border: 1px solid #d1e0e9; border-radius: 5px; color: #3c6685; background: #fff; font: inherit; font-size: .72rem; font-weight: 750; }.relationship-concepts button:hover, .confusable-concepts button:hover { border-color: #8aa9bd; background: #f1f8fb; }.relationship-source { margin: 13px 0 0; color: #7890a0; font-size: .68rem; line-height: 1.45; }.exploration-history { margin: 0 22px 22px; padding: 14px 16px; border-top: 1px solid #e1e9ee; }.exploration-history-head { display: flex; justify-content: space-between; gap: 16px; align-items: start; }.exploration-history-head span, .exploration-history-grid > section > b { color: #5d7a90; font-size: .7rem; font-weight: 850; }.exploration-history-head p { margin: 4px 0 0; color: #6c8394; font-size: .74rem; }.exploration-history-head button { padding: 5px 7px; border: 0; border-radius: 5px; color: #667f91; background: #eef3f6; font: inherit; font-size: .7rem; }.exploration-history-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 15px; margin-top: 12px; }.history-chips { display: flex; flex-wrap: wrap; gap: 6px; margin-top: 7px; }.history-chips button { padding: 5px 7px; border: 1px solid #d6e3eb; border-radius: 5px; color: #3f6683; background: #fff; font: inherit; font-size: .72rem; font-weight: 750; }.history-chips button:hover { border-color: #8aa8bc; background: #f3f8fa; }

.confusable-section { border-top: 1px solid #e1e8ed; background: #fff; }.confusable-list { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }.confusable-card { min-width: 0; padding: 17px; border: 1px solid #dae5eb; border-radius: 10px; background: #fff; }.confusable-card header > span { color: #658196; font-size: .68rem; font-weight: 850; }.confusable-card h3 { margin: 5px 0 0; color: #244f76; font-size: 1rem; }.confusable-definitions { display: grid; grid-template-columns: 1fr 1fr; gap: 8px; margin-top: 12px; }.confusable-definitions section { padding: 10px; border-radius: 7px; background: #f5f9fb; }.confusable-definitions b { color: #315d80; font-size: .78rem; }.confusable-definitions p { margin: 5px 0 0; color: #506b80; font-size: .76rem; line-height: 1.48; }.confusable-card dl { display: grid; gap: 9px; margin: 11px 0 0; }.confusable-card dl div { padding-top: 9px; border-top: 1px solid #e4ecf1; }.confusable-card dt { color: #6c8394; font-size: .68rem; font-weight: 850; }.confusable-card dd { margin: 4px 0 0; color: #425e74; font-size: .77rem; line-height: 1.52; }.confusable-card .confusable-condition { border-top-color: #e5e2c8; }.confusable-card .confusable-condition dt { color: #7a7455; }.confusable-concepts { display: flex; flex-wrap: wrap; align-items: center; gap: 6px; margin-top: 12px; }.confusable-concepts > b { margin-right: 3px; color: #5e7a90; font-size: .7rem; }

@media (max-width: 760px) {
  .element-overview { grid-template-columns: 1fr 1fr; }.detail-actions { grid-column: 1 / -1; justify-content: flex-end; }.detail-top { grid-template-columns: auto minmax(0, 1fr); }.detail-close { margin-left: 0; }.compare-cards, .relationship-facts-grid, .relationship-insights, .confusable-list { grid-template-columns: 1fr; }.comparison-picker { grid-template-columns: 1fr; align-items: stretch; }.comparison-picker > span { display: none; }.comparison-picker button { width: 100%; }.exploration-history-grid { grid-template-columns: 1fr; }
}
@media (max-width: 600px) {
  .quick-elements { gap: 5px; }.quick-elements > span { flex-basis: 100%; }.quick-elements button { font-size: .68rem; }.filter-note { font-size: .75rem; }.detail-actions { gap: 6px; }.compare-toggle { padding: 7px 8px; }.element-overview { grid-template-columns: 1fr; margin-right: 15px; margin-left: 15px; }.orbital-map { padding: 13px; }.orbital-row { grid-template-columns: 26px minmax(0, 1fr) 37px; gap: 5px; }.orbital-boxes { gap: 3px; }.orbital-box { width: 29px; height: 30px; font-size: 1rem; }.orbital-row > span { font-size: .65rem; }.compare-panel { margin-right: 15px; margin-left: 15px; padding: 14px; }.compare-heading, .relationship-title, .exploration-history-head { display: block; }.compare-clear, .relationship-save, .exploration-history-head button { margin-top: 10px; }.compare-card dl, .relationship-facts-card dl, .confusable-definitions { grid-template-columns: 1fr 1fr; }.exploration-history { margin-right: 15px; margin-left: 15px; padding-right: 0; padding-left: 0; }
}