*,
*::before,
*::after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

:root {
  --accent: #2563eb;
  --accent-light: #dbeafe;
  --text: #1e293b;
  --text-secondary: #64748b;
  --bg: #ffffff;
  --bg-subtle: #f8fafc;
  --border: #e2e8f0;
  --radius: 12px;
  --max-width: 720px;
}

html {
  font-size: 16px;
  scroll-behavior: smooth;
}

body {
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, sans-serif;
  color: var(--text);
  background: var(--bg);
  line-height: 1.7;
  -webkit-font-smoothing: antialiased;
}

/* ── Navigation ── */
nav {
  position: sticky;
  top: 0;
  z-index: 100;
  background: rgba(255, 255, 255, 0.85);
  backdrop-filter: blur(12px);
  -webkit-backdrop-filter: blur(12px);
  border-bottom: 1px solid var(--border);
}

nav .nav-inner {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 16px 24px;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

nav .logo {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--text);
  text-decoration: none;
  letter-spacing: -0.02em;
}

nav .logo span {
  color: var(--accent);
}

nav .nav-links {
  display: flex;
  gap: 24px;
  list-style: none;
}

nav .nav-links a {
  font-size: 0.875rem;
  font-weight: 500;
  color: var(--text-secondary);
  text-decoration: none;
  transition: color 0.2s;
}

nav .nav-links a:hover,
nav .nav-links a.active {
  color: var(--accent);
}

/* ── Hero (index page) ── */
.hero {
  text-align: center;
  padding: 80px 24px 60px;
  max-width: var(--max-width);
  margin: 0 auto;
}

.hero h1 {
  font-size: 2.5rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  line-height: 1.2;
  margin-bottom: 16px;
}

.hero p {
  font-size: 1.125rem;
  color: var(--text-secondary);
  max-width: 480px;
  margin: 0 auto 40px;
}

.hero .links {
  display: flex;
  gap: 16px;
  justify-content: center;
  flex-wrap: wrap;
}

.hero .links a {
  display: inline-flex;
  align-items: center;
  gap: 8px;
  padding: 14px 28px;
  border-radius: var(--radius);
  font-size: 0.9375rem;
  font-weight: 600;
  text-decoration: none;
  transition: all 0.2s;
}

.hero .links a.primary {
  background: var(--accent);
  color: #fff;
}

.hero .links a.primary:hover {
  background: #1d4ed8;
  transform: translateY(-1px);
  box-shadow: 0 4px 12px rgba(37, 99, 235, 0.3);
}

.hero .links a.secondary {
  background: var(--bg-subtle);
  color: var(--text);
  border: 1px solid var(--border);
}

.hero .links a.secondary:hover {
  background: var(--accent-light);
  border-color: var(--accent);
  color: var(--accent);
}

/* ── Content pages ── */
.content {
  max-width: var(--max-width);
  margin: 0 auto;
  padding: 48px 24px 80px;
}

.content .page-header {
  margin-bottom: 40px;
  padding-bottom: 24px;
  border-bottom: 1px solid var(--border);
}

.content .page-header h1 {
  font-size: 2rem;
  font-weight: 800;
  letter-spacing: -0.03em;
  margin-bottom: 8px;
}

.content .page-header .subtitle {
  font-size: 0.9375rem;
  color: var(--text-secondary);
}

.content h2 {
  font-size: 1.25rem;
  font-weight: 700;
  margin-top: 40px;
  margin-bottom: 12px;
  letter-spacing: -0.01em;
}

.content h3 {
  font-size: 1.0625rem;
  font-weight: 600;
  margin-top: 28px;
  margin-bottom: 8px;
}

.content p {
  margin-bottom: 16px;
  color: var(--text);
}

.content ul,
.content ol {
  margin-bottom: 16px;
  padding-left: 24px;
}

.content li {
  margin-bottom: 8px;
}

.content a {
  color: var(--accent);
  text-decoration: none;
  font-weight: 500;
}

.content a:hover {
  text-decoration: underline;
}

.content .highlight-box {
  background: var(--accent-light);
  border-left: 4px solid var(--accent);
  border-radius: 0 var(--radius) var(--radius) 0;
  padding: 16px 20px;
  margin: 24px 0;
  font-size: 0.9375rem;
}

/* ── Footer ── */
footer {
  border-top: 1px solid var(--border);
  padding: 32px 24px;
  text-align: center;
  color: var(--text-secondary);
  font-size: 0.8125rem;
}

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

footer a:hover {
  color: var(--accent);
}

footer .footer-links {
  margin-top: 8px;
  display: flex;
  gap: 24px;
  justify-content: center;
}

/* ── Responsive ── */
@media (max-width: 640px) {
  .hero h1 {
    font-size: 1.75rem;
  }

  .hero .links {
    flex-direction: column;
    align-items: center;
  }

  .hero .links a {
    width: 100%;
    max-width: 280px;
    justify-content: center;
  }

  .content .page-header h1 {
    font-size: 1.5rem;
  }

  nav .nav-links {
    gap: 16px;
  }
}