/* Base Reset & Core Styles */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
}

body {
  background-color: var(--bg-primary);
  color: var(--text-primary);
  line-height: 1.6;
  overflow-x: hidden;
  transition: var(--transition);
}

a {
  color: var(--accent-cyan);
  text-decoration: none;
  transition: var(--transition);
}
a:hover { opacity: 0.85; }

/* Sticky Header */
header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: rgba(10, 12, 16, 0.85);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-color);
  padding: 0.85rem 2rem;
  display: flex;
  justify-content: space-between;
  align-items: center;
}

[data-theme="light"] header {
  background: rgba(248, 250, 252, 0.85);
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  font-weight: 800;
  font-size: 1.4rem;
}

.nav-links {
  display: flex;
  gap: 1rem;
  list-style: none;
  align-items: center;
}

.nav-links a {
  color: var(--text-secondary);
  font-size: 0.9rem;
  font-weight: 500;
  padding: 0.35rem 0.6rem;
  border-radius: 6px;
}

.nav-links a:hover, .nav-links a.active {
  color: var(--text-primary);
  background: rgba(255, 255, 255, 0.05);
}

/* Footer */
footer {
  border-top: 1px solid var(--border-color);
  padding: 3.5rem 2rem 2rem;
  background: var(--bg-secondary);
  margin-top: 5rem;
}

.footer-grid {
  max-width: 1200px;
  margin: 0 auto;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(180px, 1fr));
  gap: 2rem;
  margin-bottom: 2.5rem;
}

.footer-col h4 { margin-bottom: 1rem; font-size: 1rem; }
.footer-col ul { list-style: none; }
.footer-col li { margin-bottom: 0.5rem; }
.footer-col a { color: var(--text-secondary); font-size: 0.9rem; }
.footer-bottom {
  text-align: center;
  color: var(--text-muted);
  font-size: 0.85rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border-color);
  display: flex;
  justify-content: space-between;
  align-items: center;
  max-width: 1200px;
  margin: 0 auto;
  flex-wrap: wrap;
  gap: 1rem;
}
.back-to-top {
  background: var(--bg-card);
  border: 1px solid var(--border-color);
  color: var(--text-primary);
  padding: 0.4rem 1rem;
  border-radius: 20px;
  cursor: pointer;
  font-size: 0.85rem;
}