/* Lithium Battery Atlas — light encyclopedia design system */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
:root {
  --paper: #fbfaf6;
  --paper-2: #f2f6f9;
  --ink: #172033;
  --muted: #64748b;
  --line: #dce5ee;
  --card: #ffffff;
  --blue: #2563eb;
  --cyan: #0891b2;
  --green: #16a34a;
  --amber: #f59e0b;
  --violet: #7c3aed;
  --red: #dc2626;
  --shadow: 0 18px 55px rgba(22, 32, 51, 0.10);
  --radius: 20px;
  --transition: 0.24s ease;
  --sans: 'Inter', system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  --serif: 'Source Serif 4', Georgia, serif;
  --mono: 'JetBrains Mono', 'SFMono-Regular', Consolas, monospace;
}
html { scroll-behavior: smooth; }
body {
  color: var(--ink);
  font-family: var(--sans);
  line-height: 1.72;
  background:
    radial-gradient(circle at 8% 0%, rgba(37,99,235,0.10), transparent 32rem),
    radial-gradient(circle at 90% 10%, rgba(22,163,74,0.10), transparent 28rem),
    linear-gradient(180deg, #fffefa, var(--paper));
  overflow-x: hidden;
}
a { color: var(--blue); text-decoration: none; transition: color var(--transition); }
a:hover { color: var(--green); }
img { max-width: 100%; display: block; }
:focus-visible { outline: 3px solid rgba(37,99,235,.35); outline-offset: 3px; border-radius: 8px; }
.site-header {
  position: fixed; top: 0; left: 0; right: 0; z-index: 1000;
  min-height: 70px; display: flex; align-items: center; justify-content: space-between;
  padding: 0 1.6rem; background: rgba(255,255,255,.82); backdrop-filter: blur(18px);
  border-bottom: 1px solid rgba(220,229,238,.76); transition: box-shadow var(--transition), background var(--transition);
}
.site-header.scrolled { background: rgba(255,255,255,.96); box-shadow: 0 10px 32px rgba(22,32,51,.08); }
.logo { display: inline-flex; align-items: center; gap: .55rem; color: var(--ink); font-weight: 900; letter-spacing: -.035em; font-size: 1.18rem; }
.logo-mark { width: 32px; height: 32px; border-radius: 10px; display: grid; place-items: center; color: white; background: linear-gradient(135deg, var(--blue), var(--green)); box-shadow: 0 8px 22px rgba(37,99,235,.22); }
.nav-links { display: flex; align-items: center; gap: .82rem; list-style: none; }
.nav-links a { color: var(--muted); font-weight: 750; font-size: .83rem; padding: .45rem .2rem; border-bottom: 2px solid transparent; }
.nav-links a:hover, .nav-links a.active { color: var(--blue); border-bottom-color: var(--blue); }
.nav-toggle { display: none; border: 0; background: var(--paper-2); border-radius: 12px; padding: .55rem; cursor: pointer; }
.nav-toggle span { display: block; width: 24px; height: 2px; background: var(--ink); margin: 5px 0; border-radius: 999px; }
section { padding: 5.8rem 1.4rem; }
.container, .article-layout, .footer-grid, .stats-grid, .topic-grid, .timeline, .quick-grid { width: min(1160px, 100%); margin: 0 auto; }
.hero { min-height: 92vh; display: grid; align-items: center; padding: 8rem 1.4rem 5rem; }
.hero-inner { width: min(1160px, 100%); margin: 0 auto; display: grid; grid-template-columns: 1.04fr .96fr; gap: 3rem; align-items: center; }
.eyebrow, .section-label, .tag, .filter-btn { display: inline-flex; align-items: center; gap: .4rem; width: fit-content; font-family: var(--mono); font-size: .73rem; letter-spacing: .09em; text-transform: uppercase; color: var(--blue); border: 1px solid rgba(37,99,235,.18); background: rgba(37,99,235,.07); border-radius: 999px; padding: .38rem .72rem; }
h1, h2, h3 { line-height: 1.12; letter-spacing: -.035em; }
h1 { font-size: clamp(2.6rem, 6vw, 5.3rem); margin: 1rem 0 1.2rem; }
.hero h1 span, .page-hero h1 span { background: linear-gradient(135deg, var(--blue), var(--green)); -webkit-background-clip: text; color: transparent; }
.lead { color: var(--muted); font-size: 1.12rem; max-width: 700px; }
.hero-actions { display: flex; flex-wrap: wrap; gap: .85rem; margin-top: 2rem; }
.btn { display: inline-flex; align-items: center; justify-content: center; gap: .48rem; border-radius: 999px; padding: .78rem 1.25rem; border: 1px solid var(--line); background: white; color: var(--ink); font-weight: 850; box-shadow: 0 8px 25px rgba(22,32,51,.07); transition: transform var(--transition), box-shadow var(--transition), background var(--transition); cursor: pointer; }
.btn:hover { transform: translateY(-2px); box-shadow: 0 14px 34px rgba(22,32,51,.12); }
.btn-primary { color: white; background: linear-gradient(135deg, var(--blue), var(--cyan)); border-color: transparent; }
.hero-visual, .diagram-card, .card, .topic-card, .stat-box, .table-wrap, .callout, .glossary-card, .faq-item { background: var(--card); border: 1px solid var(--line); border-radius: var(--radius); box-shadow: var(--shadow); }
.hero-visual { padding: .9rem; overflow: hidden; transform: rotate(-1.5deg); }
.hero-visual img { border-radius: calc(var(--radius) - 8px); width: 100%; }
.page-hero { padding: 8.5rem 1.4rem 4rem; text-align: center; background: linear-gradient(180deg, rgba(37,99,235,.07), transparent); border-bottom: 1px solid rgba(220,229,238,.55); }
.page-hero p { margin: 0 auto; }
.breadcrumb { margin-top: 1.2rem; color: var(--muted); font-size: .9rem; display: flex; justify-content: center; gap: .5rem; }
.section-head { max-width: 760px; margin: 0 auto 3rem; text-align: center; }
.section-head h2 { font-size: clamp(1.9rem, 4vw, 3.1rem); margin: .9rem 0; }
.topic-grid { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1.2rem; }
.quick-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 1rem; }
.card, .topic-card, .diagram-card, .glossary-card { padding: 1.35rem; transition: transform var(--transition), box-shadow var(--transition), border-color var(--transition); }
.card:hover, .topic-card:hover, .glossary-card:hover { transform: translateY(-5px); border-color: rgba(37,99,235,.25); box-shadow: 0 24px 60px rgba(37,99,235,.11); }
.card h3, .topic-card h3, .glossary-card h3 { margin-bottom: .55rem; }
.card p, .topic-card p, .glossary-card p, .caption, .muted { color: var(--muted); }
.icon { width: 48px; height: 48px; display: grid; place-items: center; border-radius: 15px; background: linear-gradient(135deg, rgba(37,99,235,.12), rgba(22,163,74,.10)); font-size: 1.55rem; margin-bottom: .85rem; }
.stats-grid { display: grid; grid-template-columns: repeat(4,1fr); gap: 1rem; }
.stat-box { padding: 1.25rem; text-align: center; }
.stat-number { font-size: 2.15rem; font-weight: 950; color: var(--blue); letter-spacing: -.05em; }
.stat-label { color: var(--muted); font-size: .9rem; }
.article-layout { display: grid; grid-template-columns: minmax(0, 1fr) 320px; gap: 2rem; align-items: start; }
.article-main { min-width: 0; }
.article-main > * + * { margin-top: 1.05rem; }
.article-main h2 { font-size: clamp(1.55rem, 3vw, 2.25rem); margin-top: 2.2rem; }
.article-main h3 { font-size: 1.28rem; margin-top: 1.5rem; }
.article-main p, .article-main li { color: #334155; }
.article-main ul { padding-left: 1.2rem; }
.article-main strong { color: var(--ink); }
.side-note { position: sticky; top: 92px; display: grid; gap: 1rem; }
.callout { padding: 1.1rem; border-left: 5px solid var(--blue); background: #f8fbff; }
.diagram-card { padding: .85rem; }
.diagram-card img { width: 100%; border-radius: 14px; background: #f8fafc; }
.caption { padding: .75rem .2rem .1rem; font-size: .88rem; }
.timeline { display: grid; gap: 1rem; }
.timeline-item { display: grid; grid-template-columns: 110px 1fr; gap: 1rem; align-items: start; }
.timeline-year { font-weight: 950; color: white; background: linear-gradient(135deg, var(--blue), var(--green)); border-radius: 16px; padding: .8rem; text-align: center; box-shadow: 0 10px 24px rgba(37,99,235,.16); }
.timeline-body { background: white; border: 1px solid var(--line); border-radius: 16px; padding: 1rem; }
.table-wrap { overflow-x: auto; }
table { width: 100%; border-collapse: collapse; background: white; }
th, td { padding: .9rem; border-bottom: 1px solid var(--line); text-align: left; vertical-align: top; }
th { color: var(--ink); background: #f4f8fc; font-size: .86rem; text-transform: uppercase; letter-spacing: .04em; }
.tag-row { display: flex; flex-wrap: wrap; gap: .45rem; margin-top: .75rem; }
.tag.green { color: var(--green); border-color: rgba(22,163,74,.20); background: rgba(22,163,74,.07); }
.tag.amber { color: var(--amber); border-color: rgba(245,158,11,.22); background: rgba(245,158,11,.08); }
.tag.violet { color: var(--violet); border-color: rgba(124,58,237,.22); background: rgba(124,58,237,.08); }
.filter-row { display: flex; flex-wrap: wrap; gap: .55rem; justify-content: center; margin: 1.2rem 0 2rem; }
.filter-btn { background: white; cursor: pointer; color: var(--muted); }
.filter-btn.active, .filter-btn:hover { color: white; background: var(--blue); border-color: var(--blue); }
.search-box { width: min(660px, 100%); margin: 0 auto; display: grid; gap: .45rem; }
.search-box label { font-weight: 850; }
.search-box input { width: 100%; border: 1px solid var(--line); border-radius: 16px; padding: .95rem 1rem; font: inherit; box-shadow: 0 8px 25px rgba(22,32,51,.06); }
.glossary-grid { width: min(1160px,100%); margin: 0 auto; display: grid; grid-template-columns: repeat(3, 1fr); gap: 1rem; }
.faq-list { width: min(850px,100%); margin: 0 auto; display: grid; gap: .85rem; }
.faq-question { width: 100%; display: flex; justify-content: space-between; gap: 1rem; align-items: center; padding: 1rem 1.2rem; border: 0; background: transparent; font: inherit; font-weight: 900; color: var(--ink); cursor: pointer; text-align: left; }
.faq-answer { max-height: 0; overflow: hidden; transition: max-height var(--transition); }
.faq-answer p { padding: 0 1.2rem 1rem; color: var(--muted); }
.faq-item.open .faq-answer { max-height: 60vh; }
footer { padding: 4rem 1.4rem 2rem; background: #111827; color: #dbeafe; }
.footer-grid { display: grid; grid-template-columns: 1.4fr repeat(3,1fr); gap: 2rem; }
footer a { color: #bfdbfe; }
footer p, footer li { color: #94a3b8; }
footer ul { list-style: none; display: grid; gap: .4rem; }
.footer-bottom { width: min(1160px,100%); margin: 2rem auto 0; padding-top: 1.2rem; border-top: 1px solid rgba(255,255,255,.12); color: #94a3b8; font-size: .86rem; }
.fade-in { opacity: 1; transform: none; }
.js .fade-in { opacity: 0; transform: translateY(24px); transition: opacity .65s ease, transform .65s ease; }
.js .fade-in.visible { opacity: 1; transform: translateY(0); }
@media (max-width: 1120px) { .nav-links { gap: .45rem; } .nav-links a { font-size: .78rem; } }
@media (max-width: 960px) {
  .hero-inner, .article-layout { grid-template-columns: 1fr; }
  .topic-grid, .glossary-grid { grid-template-columns: repeat(2,1fr); }
  .quick-grid, .stats-grid, .footer-grid { grid-template-columns: repeat(2,1fr); }
  .side-note { position: static; }
  .hero-visual { transform: none; }
}
@media (max-width: 760px) {
  .site-header { padding: 0 .9rem; }
  .nav-toggle { display: block; }
  .nav-links { display: none; position: fixed; top: 76px; left: .8rem; right: .8rem; flex-direction: column; align-items: stretch; background: white; border: 1px solid var(--line); border-radius: 18px; padding: .8rem; box-shadow: var(--shadow); }
  .nav-links.open { display: flex; }
  .nav-links a { font-size: .94rem; padding: .75rem; border-bottom: 0; }
  section { padding: 4rem 1rem; }
  .hero { padding: 7rem 1rem 4rem; }
  .page-hero { padding: 7.6rem 1rem 3rem; }
  .topic-grid, .glossary-grid, .quick-grid, .stats-grid, .footer-grid { grid-template-columns: 1fr; }
  .timeline-item { grid-template-columns: 1fr; }
}