:root {
  --ink: #06295a;
  --ink-strong: #031d43;
  --text: #26364d;
  --muted: #5c6d82;
  --line: #d8e4f1;
  --blue: #0969da;
  --blue-dark: #0757b6;
  --cyan: #0aa7de;
  --teal: #08a99a;
  --red: #ef493d;
  --soft: #f4f9ff;
  --white: #ffffff;
  --shadow: 0 18px 60px rgba(4, 43, 91, 0.1);
  --radius: 1.25rem;
  --max: 74rem;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  color: var(--text);
  background: var(--white);
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  line-height: 1.65;
  text-rendering: optimizeLegibility;
}
img { max-width: 100%; height: auto; }
a { color: var(--blue-dark); text-underline-offset: 0.2em; }
a:hover { color: var(--ink); }
button, input { font: inherit; }

.skip-link {
  position: fixed;
  z-index: 1000;
  top: 0.75rem;
  left: 0.75rem;
  transform: translateY(-180%);
  background: var(--ink-strong);
  color: var(--white);
  padding: 0.65rem 0.9rem;
  border-radius: 0.5rem;
}
.skip-link:focus { transform: translateY(0); }

.wrap { width: min(calc(100% - 2rem), var(--max)); margin-inline: auto; }
.narrow { width: min(calc(100% - 2rem), 48rem); margin-inline: auto; }

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  border-bottom: 1px solid rgba(216, 228, 241, 0.85);
  background: rgba(255, 255, 255, 0.94);
  backdrop-filter: blur(14px);
}
.header-inner { min-height: 4.5rem; display: flex; align-items: center; justify-content: space-between; gap: 1.5rem; }
.brand { display: inline-flex; align-items: center; gap: 0.7rem; text-decoration: none; color: var(--ink-strong); font-weight: 800; letter-spacing: -0.03em; font-size: 1.25rem; }
.brand img { width: 2.25rem; height: 2.25rem; object-fit: cover; border-radius: 50%; }
.site-nav { display: flex; align-items: center; gap: 1.3rem; }
.site-nav a { color: var(--text); text-decoration: none; font-weight: 650; font-size: 0.94rem; }
.site-nav a:hover, .site-nav a[aria-current="page"] { color: var(--blue); }
.nav-toggle { display: none; border: 1px solid var(--line); background: var(--white); color: var(--ink); border-radius: 0.65rem; padding: 0.55rem 0.75rem; font-weight: 700; }

.hero {
  overflow: hidden;
  border-bottom: 1px solid var(--line);
  background:
    radial-gradient(circle at 84% 18%, rgba(10, 167, 222, 0.16), transparent 25rem),
    radial-gradient(circle at 8% 88%, rgba(239, 73, 61, 0.08), transparent 22rem),
    linear-gradient(180deg, #fff 0%, #f7fbff 100%);
}
.hero-grid { min-height: 41rem; display: grid; grid-template-columns: 1.08fr 0.92fr; align-items: center; gap: 3rem; padding-block: 5rem; }
.eyebrow { margin: 0 0 1rem; color: var(--blue-dark); text-transform: uppercase; letter-spacing: 0.12em; font-weight: 800; font-size: 0.76rem; }
h1, h2, h3 { color: var(--ink-strong); line-height: 1.1; text-wrap: balance; }
h1 { margin: 0; font-size: clamp(2.75rem, 7vw, 5.6rem); letter-spacing: -0.065em; }
h2 { margin: 0 0 1rem; font-size: clamp(2rem, 4vw, 3.4rem); letter-spacing: -0.045em; }
h3 { margin: 0 0 0.55rem; font-size: 1.28rem; letter-spacing: -0.02em; }
.lede { max-width: 42rem; margin: 1.4rem 0 0; color: #3d5068; font-size: clamp(1.08rem, 2vw, 1.3rem); }
.actions { display: flex; flex-wrap: wrap; gap: 0.75rem; margin-top: 2rem; }
.button { display: inline-flex; align-items: center; justify-content: center; min-height: 3rem; padding: 0.72rem 1.1rem; border-radius: 0.75rem; text-decoration: none; font-weight: 800; }
.button-primary { color: var(--white); background: var(--blue); box-shadow: 0 10px 24px rgba(9, 105, 218, 0.2); }
.button-primary:hover { color: var(--white); background: var(--blue-dark); }
.button-secondary { color: var(--ink); background: var(--white); border: 1px solid var(--line); }
.hero-note { margin: 1.1rem 0 0; color: var(--muted); font-size: 0.92rem; }
.logo-card { position: relative; padding: 2rem; border: 1px solid rgba(216, 228, 241, 0.9); border-radius: 2rem; background: rgba(255, 255, 255, 0.82); box-shadow: var(--shadow); transform: rotate(1deg); }
.logo-card img { display: block; width: min(100%, 34rem); margin-inline: auto; }

.trust-strip { border-bottom: 1px solid var(--line); background: var(--white); }
.trust-grid { display: grid; grid-template-columns: repeat(4, 1fr); gap: 1px; background: var(--line); }
.trust-item { padding: 1.35rem; background: var(--white); }
.trust-item strong { display: block; color: var(--ink); }
.trust-item span { color: var(--muted); font-size: 0.9rem; }

.section { padding-block: 5.5rem; }
.section-soft { background: var(--soft); }
.section-head { display: flex; justify-content: space-between; align-items: end; gap: 2rem; margin-bottom: 2rem; }
.section-head p { max-width: 42rem; margin: 0; color: var(--muted); }
.grid-3 { display: grid; grid-template-columns: repeat(3, 1fr); gap: 1.25rem; }
.grid-2 { display: grid; grid-template-columns: repeat(2, 1fr); gap: 1.25rem; }
.card { padding: 1.6rem; border: 1px solid var(--line); border-radius: var(--radius); background: var(--white); box-shadow: 0 8px 30px rgba(4, 43, 91, 0.05); }
.card p:last-child { margin-bottom: 0; }
.card-kicker { color: var(--blue-dark); text-transform: uppercase; letter-spacing: 0.09em; font-weight: 800; font-size: 0.72rem; }
.icon { width: 2.5rem; height: 2.5rem; display: grid; place-items: center; margin-bottom: 1.2rem; border-radius: 0.8rem; color: var(--white); background: linear-gradient(135deg, var(--blue), var(--cyan)); font-weight: 900; }

.process { counter-reset: step; display: grid; gap: 1rem; }
.process article { position: relative; padding: 1.35rem 1.35rem 1.35rem 4.6rem; border-left: 2px solid var(--line); }
.process article::before { counter-increment: step; content: counter(step); position: absolute; top: 1.1rem; left: 1rem; display: grid; place-items: center; width: 2.4rem; height: 2.4rem; border-radius: 50%; color: var(--white); background: var(--ink); font-weight: 800; }

.callout { padding: 1.5rem; border: 1px solid #bdd8f4; border-left: 5px solid var(--blue); border-radius: 0.8rem; background: #eef7ff; }
.callout-warning { border-color: #f5d3cf; border-left-color: var(--red); background: #fff5f4; }
.status-panel { display: grid; grid-template-columns: auto 1fr; gap: 0.9rem; padding: 1.25rem; border: 1px solid var(--line); border-radius: 1rem; background: var(--white); }
.status-dot { width: 0.85rem; height: 0.85rem; margin-top: 0.35rem; border-radius: 50%; background: #e7a820; box-shadow: 0 0 0 5px #fff3cd; }

.article-header { padding: 5rem 0 3rem; background: linear-gradient(180deg, #f4f9ff, #fff); border-bottom: 1px solid var(--line); }
.article-header h1 { max-width: 54rem; font-size: clamp(2.5rem, 6vw, 4.7rem); }
.article-meta { color: var(--muted); font-size: 0.92rem; }
.prose { padding-block: 4rem 6rem; }
.prose h2 { margin-top: 2.5rem; font-size: clamp(1.65rem, 3vw, 2.3rem); }
.prose h3 { margin-top: 2rem; }
.prose p, .prose li { font-size: 1.04rem; }
.prose .formula { overflow-x: auto; padding: 1.25rem; border-radius: 0.8rem; background: var(--ink-strong); color: white; font: 700 1rem/1.6 ui-monospace, SFMono-Regular, Menlo, monospace; }
.prose .table-scroll { max-width: 100%; margin-block: 1.5rem; overflow-x: auto; border: 1px solid var(--line); border-radius: 0.8rem; }
.prose .table-scroll:focus { outline: 3px solid rgba(9, 105, 218, 0.35); outline-offset: 2px; }
.prose table { width: 100%; min-width: 44rem; border-collapse: collapse; background: var(--white); }
.prose caption { padding: 1rem; color: var(--ink); font-weight: 800; text-align: left; }
.prose th, .prose td { padding: 0.8rem; border-top: 1px solid var(--line); text-align: left; vertical-align: top; }
.prose thead th { background: var(--soft); }
.prose .sources { margin-top: 3rem; padding-top: 2rem; border-top: 1px solid var(--line); }
.prose .sources li { margin-block: 0.6rem; scroll-margin-top: 6rem; }

.learn-overview { padding-block: 4rem 6rem; }
.learn-intro { max-width: 52rem; margin-bottom: 2rem; font-size: 1.08rem; }
.letter-nav { display: flex; flex-wrap: wrap; align-items: center; gap: 0.55rem; margin-bottom: 3rem; padding: 1rem; border: 1px solid var(--line); border-radius: 0.9rem; background: var(--soft); }
.letter-nav strong { margin-right: 0.4rem; color: var(--ink); }
.letter-nav a { display: inline-grid; place-items: center; min-width: 2rem; min-height: 2rem; border: 1px solid var(--line); border-radius: 0.5rem; background: var(--white); text-decoration: none; font-weight: 800; }
.term-group { padding-top: 1rem; }
.term-group > h2 { padding-bottom: 0.65rem; border-bottom: 2px solid var(--ink); font-size: 2rem; scroll-margin-top: 6rem; }
.term-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 1rem; margin-bottom: 2.5rem; }
.term-card { padding: 1.25rem; border: 1px solid var(--line); border-radius: 1rem; background: var(--white); }
.term-card h3 { font-size: 1.12rem; }
.term-card p { margin-bottom: 0; color: var(--muted); }
.breadcrumbs { display: flex; flex-wrap: wrap; gap: 0.55rem; margin-bottom: 2rem; color: var(--muted); font-size: 0.92rem; }
.term-example { margin-top: 2rem; }
.term-links { display: flex; flex-wrap: wrap; gap: 0.65rem; }
.term-links a { padding: 0.45rem 0.7rem; border: 1px solid var(--line); border-radius: 999px; background: var(--soft); text-decoration: none; font-weight: 700; }
.related-terms { margin-top: 2.5rem; }

.site-footer { padding: 4rem 0 2rem; color: #d6e5f6; background: var(--ink-strong); }
.footer-grid { display: grid; grid-template-columns: 1.5fr 1fr 1fr; gap: 2rem; }
.site-footer h2, .site-footer h3 { color: white; }
.site-footer h2 { font-size: 1.5rem; }
.site-footer a { color: #e8f4ff; }
.footer-links { list-style: none; margin: 0; padding: 0; }
.footer-links li { margin-block: 0.45rem; }
.footer-bottom { margin-top: 2.5rem; padding-top: 1.5rem; border-top: 1px solid rgba(255,255,255,0.16); font-size: 0.86rem; color: #a9bfd7; }

@media (max-width: 860px) {
  .nav-toggle { display: inline-flex; }
  .site-nav { display: none; position: absolute; inset: 4.5rem 1rem auto; align-items: stretch; flex-direction: column; gap: 0; padding: 0.7rem; border: 1px solid var(--line); border-radius: 1rem; background: white; box-shadow: var(--shadow); }
  .site-nav[data-open="true"] { display: flex; }
  .site-nav a { padding: 0.8rem; }
  .hero-grid { min-height: auto; grid-template-columns: 1fr; padding-block: 3.5rem; }
  .logo-card { order: -1; width: min(100%, 26rem); margin-inline: auto; padding: 1rem; }
  .trust-grid { grid-template-columns: repeat(2, 1fr); }
  .grid-3, .grid-2 { grid-template-columns: 1fr; }
  .term-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .section-head { align-items: start; flex-direction: column; }
  .footer-grid { grid-template-columns: 1fr; }
}

@media (max-width: 520px) {
  .wrap, .narrow { width: min(calc(100% - 1.25rem), var(--max)); }
  .header-inner { min-height: 4rem; }
  .site-nav { inset-block-start: 4rem; }
  .brand { font-size: 1.05rem; }
  .hero-grid { gap: 2rem; }
  .trust-grid { grid-template-columns: 1fr; }
  .term-grid { grid-template-columns: 1fr; }
  .letter-nav { align-items: flex-start; }
  .section { padding-block: 4rem; }
  .card { padding: 1.3rem; }
}

@media (prefers-reduced-motion: reduce) {
  html { scroll-behavior: auto; }
  *, *::before, *::after { animation-duration: 0.01ms !important; animation-iteration-count: 1 !important; transition-duration: 0.01ms !important; }
}