/* =============================================================================
   HEADER
   ============================================================================= */

.site-header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  z-index: 100;
  padding: 1rem 0;
  transition: background var(--transition-normal), box-shadow var(--transition-normal), padding var(--transition-normal), border-color var(--transition-normal);
  border-bottom: 1px solid transparent;
}

.site-header.is-scrolled {
  background: var(--color-surface-overlay);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  box-shadow: var(--shadow-md);
  border-bottom: 1px solid var(--color-border-soft);
  padding: 0.65rem 0;
}

.site-header__inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1.5rem;
}

.brand {
  display: flex;
  align-items: center;
  gap: 0.65rem;
  font-weight: 700;
  font-size: var(--font-size-lg);
  color: var(--color-text);
}

.brand__mark {
  width: 2.1rem;
  height: 2.1rem;
  border-radius: 0.6rem;
  background: var(--gradient-primary);
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: var(--shadow-primary);
  flex-shrink: 0;
}

.brand__mark svg { width: 1.2rem; height: 1.2rem; color: #fff; }

.brand__word { font-family: var(--font-display); letter-spacing: -0.01em; }
.brand__word em {
  font-style: normal;
  background: var(--gradient-primary);
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

.nav-desktop {
  display: none;
  align-items: center;
  gap: 2rem;
}

.nav-desktop a {
  font-size: var(--font-size-sm);
  font-weight: 500;
  color: var(--color-text-secondary);
  position: relative;
  padding: 0.25rem 0;
  transition: color var(--transition-fast);
}

.nav-desktop a::after {
  content: '';
  position: absolute;
  left: 0; right: 0; bottom: -4px;
  height: 2px;
  background: var(--gradient-primary);
  border-radius: var(--radius-full);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform var(--transition-normal);
}

.nav-desktop a:hover { color: var(--color-text); }
.nav-desktop a:hover::after { transform: scaleX(1); }

.header-actions {
  display: flex;
  align-items: center;
  gap: 0.75rem;
}

.theme-toggle {
  width: 2.35rem;
  height: 2.35rem;
  border-radius: var(--radius-full);
  display: inline-flex;
  align-items: center;
  justify-content: center;
  border: 1px solid var(--color-border);
  background: var(--color-surface);
  color: var(--color-text-secondary);
  transition: border-color var(--transition-fast), color var(--transition-fast), transform var(--transition-fast);
  flex-shrink: 0;
}

.theme-toggle:hover { border-color: var(--color-primary); color: var(--color-primary); }
.theme-toggle svg { width: 1.05rem; height: 1.05rem; }
.theme-toggle .icon-moon { display: none; }
.dark .theme-toggle .icon-sun { display: none; }
.dark .theme-toggle .icon-moon { display: block; }

.nav-toggle {
  display: inline-flex;
  width: 2.35rem;
  height: 2.35rem;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  border: 1px solid var(--color-border);
  background: var(--color-surface);
}

.nav-toggle svg { width: 1.2rem; height: 1.2rem; }

@media (min-width: 900px) {
  .nav-desktop { display: flex; }
  .nav-toggle { display: none; }
}

/* Mobile nav sheet */
.nav-mobile {
  position: fixed;
  inset: 0;
  z-index: 99;
  background: var(--color-surface-overlay);
  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 2rem;
  opacity: 0;
  pointer-events: none;
  transform: translateY(-8px);
  transition: opacity var(--transition-normal), transform var(--transition-normal);
}

.nav-mobile.is-open {
  opacity: 1;
  pointer-events: auto;
  transform: translateY(0);
}

.nav-mobile a {
  font-family: var(--font-display);
  font-size: var(--font-size-2xl);
  color: var(--color-text);
}

.nav-mobile .btn { margin-top: 1rem; }

.nav-mobile-close {
  position: absolute;
  top: 1.4rem;
  right: 1.5rem;
  width: 2.35rem;
  height: 2.35rem;
  border-radius: var(--radius-full);
  border: 1px solid var(--color-border);
  display: inline-flex;
  align-items: center;
  justify-content: center;
}

.nav-mobile-close svg { width: 1.1rem; height: 1.1rem; }