:root {
  --primary: #2563eb;
  --primary-dark: #1d4ed8;
  --bg: #f8fafc;
  --card: #ffffff;
  --text: #1e293b;
  --text-light: #64748b;
  --border: #e2e8f0;
  --code-bg: #1e293b;
  --code-text: #e2e8f0;
}

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

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

nav {
  background: var(--card);
  border-bottom: 1px solid var(--border);
  padding: 0 2rem;
  position: sticky;
  top: 0;
  z-index: 100;
}

.nav-container {
  max-width: 1200px;
  margin: 0 auto;
  display: flex;
  align-items: center;
  justify-content: space-between;
  height: 64px;
}

.nav-brand {
  font-size: 1.25rem;
  font-weight: 700;
  color: var(--primary);
  text-decoration: none;
}

.nav-links {
  display: flex;
  gap: 2rem;
  list-style: none;
}

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

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

main {
  max-width: 1200px;
  margin: 0 auto;
  padding: 2rem;
}

.hero {
  text-align: center;
  padding: 4rem 2rem;
  background: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  color: white;
  border-radius: 16px;
  margin-bottom: 3rem;
}

.hero h1 {
  font-size: 3rem;
  margin-bottom: 0.5rem;
}

.hero p {
  font-size: 1.25rem;
  opacity: 0.9;
  margin-bottom: 2rem;
}

.btn {
  display: inline-block;
  padding: 0.75rem 1.5rem;
  border-radius: 8px;
  text-decoration: none;
  font-weight: 600;
  transition: all 0.2s;
  margin: 0 0.5rem;
}

.btn-primary {
  background: white;
  color: #764ba2;
}

.btn-primary:hover {
  transform: translateY(-2px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.2);
}

.btn-secondary {
  background: rgba(255,255,255,0.2);
  color: white;
  border: 1px solid rgba(255,255,255,0.3);
}

.btn-secondary:hover {
  background: rgba(255,255,255,0.3);
}

.grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(300px, 1fr));
  gap: 1.5rem;
  margin-bottom: 3rem;
}

.card {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 1.5rem;
  transition: all 0.2s;
  text-decoration: none;
  color: inherit;
}

.card:hover {
  transform: translateY(-4px);
  box-shadow: 0 8px 24px rgba(0,0,0,0.08);
  border-color: var(--primary);
}

.card-icon {
  font-size: 2rem;
  margin-bottom: 0.75rem;
}

.card h3 {
  font-size: 1.125rem;
  margin-bottom: 0.5rem;
  color: var(--text);
}

.card p {
  color: var(--text-light);
  font-size: 0.95rem;
}

.section-title {
  font-size: 1.75rem;
  margin-bottom: 1.5rem;
  padding-bottom: 0.5rem;
  border-bottom: 2px solid var(--border);
}

.page-header {
  margin-bottom: 2rem;
}

.page-header h1 {
  font-size: 2rem;
  margin-bottom: 0.5rem;
}

.page-header p {
  color: var(--text-light);
}

.content {
  background: var(--card);
  border: 1px solid var(--border);
  border-radius: 12px;
  padding: 2rem;
}

.content h2 {
  font-size: 1.5rem;
  margin: 2rem 0 1rem;
  padding-bottom: 0.5rem;
  border-bottom: 1px solid var(--border);
}

.content h2:first-child {
  margin-top: 0;
}

.content h3 {
  font-size: 1.125rem;
  margin: 1.5rem 0 0.75rem;
  color: var(--primary-dark);
}

.content p {
  margin-bottom: 1rem;
}

.content ul, .content ol {
  margin: 1rem 0 1rem 1.5rem;
}

.content li {
  margin-bottom: 0.5rem;
}

.content blockquote {
  border-left: 4px solid var(--primary);
  padding-left: 1rem;
  margin: 1rem 0;
  color: var(--text-light);
  font-style: italic;
}

.content code {
  background: #f1f5f9;
  padding: 0.2rem 0.4rem;
  border-radius: 4px;
  font-family: 'SF Mono', Monaco, monospace;
  font-size: 0.9em;
}

.content pre {
  background: var(--code-bg);
  color: var(--code-text);
  padding: 1.25rem;
  border-radius: 8px;
  overflow-x: auto;
  margin: 1rem 0;
  font-size: 0.9rem;
  line-height: 1.6;
}

.content pre code {
  background: transparent;
  padding: 0;
  color: inherit;
}

.content table {
  width: 100%;
  border-collapse: collapse;
  margin: 1rem 0;
}

.content th, .content td {
  padding: 0.75rem;
  text-align: left;
  border: 1px solid var(--border);
}

.content th {
  background: var(--bg);
  font-weight: 600;
}

.content tr:nth-child(even) {
  background: var(--bg);
}

.content hr {
  border: none;
  border-top: 1px solid var(--border);
  margin: 2rem 0;
}

.badge {
  display: inline-block;
  padding: 0.25rem 0.75rem;
  border-radius: 20px;
  font-size: 0.85rem;
  font-weight: 500;
  margin-right: 0.5rem;
}

.badge-beginner { background: #dcfce7; color: #166534; }
.badge-intermediate { background: #fef9c3; color: #854d0e; }
.badge-advanced { background: #fee2e2; color: #991b1b; }

footer {
  text-align: center;
  padding: 2rem;
  color: var(--text-light);
  border-top: 1px solid var(--border);
  margin-top: 3rem;
}

@media (max-width: 768px) {
  .hero h1 { font-size: 2rem; }
  .nav-links { gap: 1rem; font-size: 0.9rem; }
  main { padding: 1rem; }
  .grid { grid-template-columns: 1fr; }
}