:root {
  --bg: #000;
  --text: #fff;
  --muted: #bfbfbf;
  --accent: #4da3ff;
  --border: #1f1f1f;
  --font-sans: 'Arial', 'Helvetica Neue', sans-serif;
  --max-width: 960px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background-color: var(--bg);
  color: var(--text);
  font-family: var(--font-sans);
  line-height: 1.7;
}

a {
  color: var(--accent);
  text-decoration: none;
}

a:hover,
a:focus {
  text-decoration: underline;
}

header,
main,
footer {
  width: min(100%, var(--max-width));
  margin: 0 auto;
  padding: 0 1.5rem;
}

.site-header,
.page-header {
  padding: 3rem 0 2rem;
}

.site-header h1,
.page-header h1 {
  margin: 0;
  font-size: clamp(2rem, 4vw, 3rem);
  letter-spacing: 0.04em;
}

.site-header p {
  margin: 0.75rem 0 0;
  max-width: 42rem;
  color: var(--muted);
}

.meta-list {
  list-style: none;
  padding: 0;
  margin: 2rem 0 0;
  display: flex;
  flex-wrap: wrap;
  gap: 1rem 2rem;
  font-size: 0.95rem;
  color: var(--muted);
}

.topic-list {
  list-style: none;
  padding: 0;
  margin: 3rem 0 4rem;
  display: grid;
  gap: 1.5rem;
}

.topic-card {
  border: 1px solid var(--border);
  border-radius: 0.75rem;
  padding: 1.5rem;
  background: #050505;
  transition: border-color 0.2s ease, transform 0.2s ease;
}

.topic-card:hover,
.topic-card:focus-within {
  border-color: var(--accent);
  transform: translateY(-3px);
}

.topic-card span {
  display: inline-block;
  font-size: 0.85rem;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--muted);
}

.topic-card h2 {
  margin: 0.75rem 0 0.5rem;
  font-size: 1.4rem;
}

.topic-card p {
  margin: 0;
  color: var(--muted);
}

.page-header .home-link {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  margin-bottom: 1.5rem;
  font-size: 0.95rem;
  color: var(--muted);
}

.page-header .home-link::before {
  content: '⟵';
  font-size: 1.1rem;
}

.topic-label {
  display: inline-flex;
  align-items: center;
  gap: 0.75rem;
  font-size: 0.9rem;
  letter-spacing: 0.22em;
  text-transform: uppercase;
  color: var(--muted);
  margin-bottom: 1rem;
}

.topic-content {
  padding-bottom: 4rem;
}

.topic-content h2 {
  margin-top: 0;
  font-size: clamp(1.8rem, 4vw, 2.4rem);
}

.topic-content p,
.topic-content li,
.topic-content dd {
  color: var(--text);
}

.topic-content ul,
.topic-content ol {
  padding-left: 1.2rem;
}

.topic-content li + li,
.topic-content p + p {
  margin-top: 0.75rem;
}

.topic-content ol {
  padding-left: 1.5rem;
}

.topic-content h3 {
  margin-top: 2rem;
  font-size: 1.3rem;
}

.reference-columns {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 1.5rem;
  padding: 0;
  list-style: none;
}

.reference-columns h3 {
  margin: 0 0 0.75rem;
  font-size: 1.1rem;
}

.reference-columns ul {
  list-style: disc;
  padding-left: 1.2rem;
}

dl {
  margin: 0;
  display: grid;
  grid-template-columns: minmax(140px, 200px) 1fr;
  gap: 0.75rem 1.5rem;
}

dl dt {
  font-weight: bold;
  color: var(--muted);
}

footer {
  padding: 3rem 1.5rem 4rem;
  color: var(--muted);
  font-size: 0.9rem;
  text-align: center;
}

@media (max-width: 640px) {
  header,
  main,
  footer {
    padding: 0 1.25rem;
  }

  dl {
    grid-template-columns: 1fr;
  }
}