/* ===========================================
   Header – Trusted Blue Palette
   =========================================== */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: var(--header-height);
  z-index: var(--z-sticky);
  /* Frosted glass effect using the page background */
  background: rgba(248, 250, 252, 0.85);      /* --color-bg with opacity */
  backdrop-filter: blur(12px) saturate(180%);
  -webkit-backdrop-filter: blur(12px) saturate(180%);
  border-bottom: 1px solid rgba(226, 232, 240, 0.6); /* --color-border with opacity */
  transition: all var(--transition-base);
}

[data-theme="dark"] .header {
  background: rgba(15, 23, 42, 0.85);          /* dark slate */
  border-bottom-color: rgba(51, 65, 85, 0.6);
}

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

.header-inner {
  height: 100%;
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: var(--space-8);
}

.logo {
  display: flex;
  align-items: center;
  gap: var(--space-2);
  font-weight: var(--weight-bold);
  font-size: var(--text-xl);
  color: var(--color-text);
  letter-spacing: -0.02em;
}

.logo-icon {
  width: 32px;
  height: 32px;
  background: linear-gradient(135deg, var(--color-primary), #60A5FA); /* blue gradient */
  border-radius: var(--radius-md);
  display: flex;
  align-items: center;
  justify-content: center;
  color: white;
  font-weight: var(--weight-bold);
  box-shadow: 0 2px 6px rgba(37, 99, 235, 0.25); /* subtle glow */
}

.nav {
  display: flex;
  align-items: center;
  gap: var(--space-6);
  flex: 1;
  justify-content: center;
}

.nav-link {
  position: relative;
  padding: var(--space-2) var(--space-3);
  color: var(--color-text-secondary);
  font-weight: var(--weight-medium);
  font-size: var(--text-sm);
  transition: color var(--transition-fast);
  border-radius: var(--radius-md);
}

.nav-link:hover,
.nav-link:focus-visible {
  color: var(--color-text);
}

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

.nav-link.active::after {
  content: '';
  position: absolute;
  bottom: -12px;
  left: 50%;
  transform: translateX(-50%);
  width: 4px;
  height: 4px;
  background: var(--color-primary);
  border-radius: var(--radius-full);
}

.header-actions {
  display: flex;
  align-items: center;
  gap: var(--space-3);
}

.header-btn {
  width: 36px;
  height: 36px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius-md);
  color: var(--color-text-secondary);
  transition: all var(--transition-fast);
}

.header-btn:hover {
  background: var(--color-card);
  color: var(--color-text);
  box-shadow: var(--shadow-sm);
}

.mobile-toggle {
  display: none;
  width: 36px;
  height: 36px;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 4px;
}

.mobile-toggle span {
  width: 18px;
  height: 2px;
  background: var(--color-text);
  border-radius: 2px;
  transition: all var(--transition-base);
}

.mobile-toggle.active span:nth-child(1) {
  transform: rotate(45deg) translate(3px, 3px);
}
.mobile-toggle.active span:nth-child(2) {
  opacity: 0;
}
.mobile-toggle.active span:nth-child(3) {
  transform: rotate(-45deg) translate(3px, -3px);
}

.mobile-nav {
  position: fixed;
  top: var(--header-height);
  left: 0;
  right: 0;
  background: var(--color-card);
  border-bottom: 1px solid var(--color-border);
  box-shadow: var(--shadow-lg);
  transform: translateY(-100%);
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-spring);
  padding: var(--space-6);
}

.mobile-nav.active {
  transform: translateY(0);
  opacity: 1;
  visibility: visible;
}

.mobile-nav-links {
  display: flex;
  flex-direction: column;
  gap: var(--space-1);
}

.mobile-nav-link {
  padding: var(--space-3) var(--space-4);
  border-radius: var(--radius-md);
  color: var(--color-text);
  font-weight: var(--weight-medium);
  transition: background var(--transition-fast);
}

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