:root {
  --teal: #14B8A6;
  --teal-dark: #0D9488;
  --text: #1a1a1a;
  --muted: #6b7280;
  --border: #e5e7eb;
  --bg: #ffffff;
}

*, *::before, *::after {
  box-sizing: border-box;
}

html {
  font-size: 16px;
}

body {
  margin: 0;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Helvetica, Arial, sans-serif;
  line-height: 1.75;
}

/* ── Nav ── */

nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 24px;
  height: 56px;
}

.nav-brand {
  font-weight: 700;
  font-size: 1.05rem;
  color: var(--text);
  letter-spacing: -0.01em;
}

.nav-links {
  display: flex;
  gap: 24px;
}

.nav-links a {
  color: var(--muted);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  transition: color 0.15s;
}

.nav-links a:hover {
  color: var(--teal);
}

.nav-links a.active {
  color: var(--teal);
}

/* ── Main content ── */

main {
  max-width: 760px;
  margin: 0 auto;
  padding: 48px 24px 64px;
}

/* ── Typography ── */

h1 {
  font-size: 2rem;
  font-weight: 700;
  color: var(--text);
  letter-spacing: -0.02em;
  line-height: 1.2;
  margin: 0 0 8px;
}

h2 {
  font-size: 1.2rem;
  font-weight: 600;
  color: var(--text);
  border-bottom: 2px solid var(--teal);
  padding-bottom: 6px;
  margin: 48px 0 16px;
  letter-spacing: -0.01em;
}

h3 {
  font-size: 1rem;
  font-weight: 600;
  color: var(--muted);
  margin: 24px 0 8px;
}

p {
  font-size: 1rem;
  margin: 0 0 16px;
  color: var(--text);
}

ul, ol {
  margin: 0 0 16px;
  padding-left: 24px;
}

li {
  margin-bottom: 6px;
}

strong {
  font-weight: 600;
  color: #111;
}

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

a:hover {
  text-decoration: underline;
}

/* ── Index page cards ── */

.intro {
  color: var(--muted);
  font-size: 1.05rem;
  margin: 16px 0 48px;
}

.cards {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
}

.card {
  display: block;
  border: 2px solid var(--border);
  border-radius: 12px;
  padding: 28px 24px;
  text-decoration: none;
  color: var(--text);
  transition: border-color 0.2s, box-shadow 0.2s;
}

.card:hover {
  border-color: var(--teal);
  box-shadow: 0 4px 16px rgba(20, 184, 166, 0.12);
  text-decoration: none;
}

.card-title {
  font-size: 1.1rem;
  font-weight: 600;
  color: var(--teal);
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 8px;
}

.card-title .arrow {
  font-size: 1.2rem;
  transition: transform 0.2s;
}

.card:hover .arrow {
  transform: translateX(4px);
}

.card-desc {
  font-size: 0.9rem;
  color: var(--muted);
  line-height: 1.5;
  margin: 0;
}

/* ── Loading state ── */

.loading {
  color: var(--muted);
  font-style: italic;
}

/* ── Footer ── */

footer {
  margin-top: 64px;
  border-top: 1px solid var(--border);
  padding: 32px 24px;
  text-align: center;
}

footer p {
  margin: 0;
  font-size: 0.875rem;
  color: var(--muted);
}

footer a {
  color: var(--teal);
}

footer a:hover {
  text-decoration: underline;
}

/* ── Responsive ── */

@media (max-width: 600px) {
  nav {
    flex-direction: column;
    align-items: flex-start;
    height: auto;
    padding: 14px 16px;
    gap: 8px;
  }

  .nav-links {
    gap: 16px;
  }

  main {
    padding: 32px 16px 48px;
  }

  h1 {
    font-size: 1.6rem;
  }

  .cards {
    grid-template-columns: 1fr;
  }
}