/* css/header.css */
.site-header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: var(--bg-glass);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border-color);
  transition: background-color 0.3s ease, border-color 0.3s ease, box-shadow 0.3s ease;
}

.site-header.scrolled {
  box-shadow: var(--shadow-md);
}

.header-container {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0.85rem 1.5rem;
  display: flex;
  align-items: center;
  justify-content: space-between;
}

/* Brand Logo */
.brand-logo {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  transition: transform 0.2s ease;
}

.brand-logo:hover {
  transform: translateY(-1px);
}

.logo-icon {
  width: 42px;
  height: 42px;
  background: linear-gradient(135deg, var(--brand-primary), var(--brand-accent));
  color: #ffffff;
  border-radius: 12px;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-glow);
}

.logo-text-group {
  display: flex;
  flex-direction: column;
}

.logo-title {
  font-size: 1.35rem;
  font-weight: 800;
  color: var(--text-main);
  line-height: 1.1;
  letter-spacing: -0.02em;
}

.logo-title .highlight {
  color: var(--brand-primary);
}

.logo-tagline {
  font-size: 0.72rem;
  font-weight: 600;
  color: var(--text-muted);
  text-transform: uppercase;
  letter-spacing: 0.06em;
}

/* Navigation Links */
.nav-list {
  display: flex;
  align-items: center;
  gap: 2rem;
  list-style: none;
}

.nav-link {
  font-size: 0.95rem;
  font-weight: 600;
  color: var(--text-muted);
  position: relative;
  padding: 0.4rem 0;
  transition: color 0.2s ease;
}

.nav-link:hover,
.nav-link.active {
  color: var(--brand-primary);
}

.nav-link::after {
  content: '';
  position: absolute;
  bottom: 0;
  left: 0;
  width: 0;
  height: 2px;
  background: var(--brand-primary);
  border-radius: 2px;
  transition: width 0.3s cubic-bezier(0.4, 0, 0.2, 1);
}

.nav-link:hover::after,
.nav-link.active::after {
  width: 100%;
}

/* Header Actions */
.header-actions {
  display: flex;
  align-items: center;
  gap: 1rem;
}

.theme-toggle-btn {
  background: var(--bg-surface);
  border: 1px solid var(--border-color);
  color: var(--text-main);
  width: 40px;
  height: 40px;
  border-radius: 10px;
  cursor: pointer;
  display: flex;
  align-items: center;
  justify-content: center;
  transition: all 0.2s ease;
}

.theme-toggle-btn:hover {
  border-color: var(--brand-primary);
  color: var(--brand-primary);
  transform: rotate(15deg);
}

[data-theme="dark"] .sun-icon { display: block; }
[data-theme="dark"] .moon-icon { display: none; }
[data-theme="light"] .sun-icon { display: none; }
[data-theme="light"] .moon-icon { display: block; }

.mobile-toggle {
  display: none;
  flex-direction: column;
  gap: 5px;
  background: none;
  border: none;
  cursor: pointer;
  padding: 5px;
}

.mobile-toggle span {
  width: 24px;
  height: 2px;
  background-color: var(--text-main);
  border-radius: 2px;
  transition: all 0.3s ease;
}

/* Responsive Mobile Navigation */
@media (max-width: 900px) {
  .mobile-toggle { display: flex; }
  
  .nav-menu {
    position: fixed;
    top: 65px;
    left: 0;
    right: 0;
    background: var(--bg-surface);
    border-bottom: 1px solid var(--border-color);
    padding: 1.5rem;
    transform: translateY(-150%);
    opacity: 0;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    box-shadow: var(--shadow-md);
  }

  .nav-menu.open {
    transform: translateY(0);
    opacity: 1;
  }

  .nav-list {
    flex-direction: column;
    align-items: flex-start;
    gap: 1.25rem;
  }
}