:root {
  --bg: #f7f7f5;
  --surface: #ffffff;
  --ink: #1a1a1a;
  --muted: #5a5a5a;
  --accent: #0a3d62;
  --accent-ink: #ffffff;
  --border: #e2e2dd;
  --example-bg: #f0f4f8;
  --max-width: 760px;
}

* {
  box-sizing: border-box;
}

html {
  -webkit-text-size-adjust: 100%;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family:
    -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial,
    sans-serif;
  font-size: 17px;
  line-height: 1.6;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 10;
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 14px 20px;
  background: var(--accent);
  color: var(--accent-ink);
}

.brand {
  display: flex;
  flex-direction: column;
  line-height: 1.25;
}

.brand-name {
  font-weight: 700;
  font-size: 1.05rem;
  letter-spacing: 0.02em;
}

.brand-sub {
  font-size: 0.8rem;
  opacity: 0.85;
}

.lang-switch {
  display: inline-flex;
  border: 1px solid rgba(255, 255, 255, 0.5);
  border-radius: 999px;
  overflow: hidden;
}

.lang-btn {
  appearance: none;
  border: 0;
  background: transparent;
  color: var(--accent-ink);
  padding: 6px 16px;
  font: inherit;
  font-size: 0.9rem;
  cursor: pointer;
}

.lang-btn[aria-pressed="true"] {
  background: var(--accent-ink);
  color: var(--accent);
  font-weight: 600;
}

main {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 32px 20px 48px;
}

.terms {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 10px;
  padding: 32px clamp(20px, 5vw, 44px);
}

.terms[hidden] {
  display: none;
}

h1 {
  font-size: 1.7rem;
  margin: 0 0 0.5em;
  color: var(--accent);
}

.intro {
  color: var(--muted);
}

h2 {
  font-size: 1.2rem;
  margin: 1.8em 0 0.4em;
  border-bottom: 1px solid var(--border);
  padding-bottom: 0.2em;
}

.appendix-title {
  color: var(--accent);
  border-bottom: 2px solid var(--accent);
}

h3 {
  font-size: 1.08rem;
  margin: 1.5em 0 0.3em;
}

h4 {
  font-size: 0.98rem;
  margin: 1.1em 0 0.2em;
  color: var(--muted);
}

p,
ul {
  margin: 0.5em 0;
}

ul {
  padding-left: 1.4em;
}

li {
  margin: 0.25em 0;
}

.formula {
  font-family: ui-monospace, SFMono-Regular, Menlo, Consolas, monospace;
  background: var(--example-bg);
  padding: 8px 12px;
  border-radius: 6px;
  display: inline-block;
}

.example {
  background: var(--example-bg);
  border-left: 3px solid var(--accent);
  padding: 8px 12px;
  border-radius: 0 6px 6px 0;
  font-size: 0.95rem;
}

hr {
  border: 0;
  border-top: 1px solid var(--border);
  margin: 2.4em 0;
}

.site-footer {
  text-align: center;
  color: var(--muted);
  font-size: 0.85rem;
  padding: 24px 20px 40px;
}

@media (max-width: 480px) {
  body {
    font-size: 16px;
  }
  .brand-name {
    font-size: 0.95rem;
  }
}

/* Print: show both languages, hide chrome */
@media print {
  .site-header,
  .site-footer {
    display: none;
  }
  body {
    background: #fff;
    font-size: 11pt;
  }
  main {
    max-width: none;
    padding: 0;
  }
  .terms {
    border: 0;
    border-radius: 0;
    padding: 0;
  }
  .terms[hidden] {
    display: block !important;
  }
  section {
    break-inside: avoid;
  }
}