#site-header {
  background-image:
    linear-gradient(var(--c-grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--c-grid-line) 1px, transparent 1px),
    linear-gradient(var(--c-header-bg), var(--c-header-bg));
  background-size:
    64px 64px,
    64px 64px,
    auto;
  background-attachment: fixed, fixed, scroll;
}

.nav-link {
  transition: color 0.18s ease;
}

.nav-link:hover,
.nav-item:hover > .nav-link {
  color: var(--c-highlight) !important;
}

.nav-label-wrap {
  display: inline-block;
}

.nav-underline {
  position: absolute;
  left: 0;
  right: 0;
  bottom: -4px;
  height: 2px;
  border-radius: 9999px;
  background: var(--c-highlight);
  transform: scaleX(0);
  transform-origin: left;
  transition: transform 0.22s ease;
}

.nav-link:hover .nav-underline,
.nav-active .nav-underline,
.nav-item:hover > .nav-link .nav-underline {
  transform: scaleX(1);
}

.nav-chevron {
  transition: transform 0.2s ease;
  flex-shrink: 0;
}

.nav-item:hover .nav-chevron {
  transform: rotate(180deg);
}

.nav-dropdown {
  position: absolute;
  top: calc(100% + 2px);
  left: 0;
  min-width: 148px;
  background: var(--c-header-bg);
  backdrop-filter: blur(14px);
  -webkit-backdrop-filter: blur(14px);
  border: 1px solid var(--c-border);
  border-radius: 8px;
  padding: 4px;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-4px);
  transition:
    opacity 0.14s ease,
    transform 0.14s ease,
    visibility 0s linear 0.14s;
  z-index: 200;
}

.nav-item:hover .nav-dropdown {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
  transition:
    opacity 0.14s ease,
    transform 0.14s ease,
    visibility 0s linear 0s;
}

.nav-dropdown-item {
  display: block;
  padding: 7px 10px;
  border-radius: 5px;
  font-size: 0.875rem;
  font-weight: 400;
  color: var(--c-muted);
  transition:
    color 0.12s ease,
    background 0.12s ease;
  white-space: nowrap;
}

.nav-dropdown-item:hover {
  color: var(--c-text);
  background: var(--c-accent-bg);
}

.nav-dropdown-item.is-active {
  color: var(--c-highlight);
}

.lang-btn:hover {
  color: var(--c-highlight) !important;
}

.theme-btn:hover {
  color: var(--c-highlight) !important;
}

.burger-btn:hover {
  color: var(--c-highlight) !important;
  background: var(--c-accent-bg) !important;
}

#site-header.scrolled {
  box-shadow: 0 4px 28px rgba(0, 0, 0, 0.15);
}

/* ── Mobile nav overlay ── */
#mobile-nav {
  position: absolute;
  left: 0;
  right: 0;
  top: 100%;
  opacity: 0;
  visibility: hidden;
  transform: translateY(-8px);
  transition:
    opacity 0.22s ease,
    transform 0.22s ease,
    visibility 0s linear 0.22s;
  z-index: 10;

  /* Blueprint panel */
  background-image:
    linear-gradient(var(--c-grid-line) 1px, transparent 1px),
    linear-gradient(90deg, var(--c-grid-line) 1px, transparent 1px),
    linear-gradient(var(--c-surface), var(--c-surface));
  background-size: 64px 64px, 64px 64px, auto;
  background-attachment: fixed, fixed, scroll;
  border-top: 1px solid var(--c-accent-border);
  box-shadow:
    0 16px 40px rgba(8, 145, 178, 0.12),
    0 4px 16px rgba(0, 0, 0, 0.08);
}

#mobile-nav.is-open {
  opacity: 1;
  visibility: visible;
  transform: translateY(0);
  transition:
    opacity 0.22s ease,
    transform 0.22s ease,
    visibility 0s linear 0s;
}

/* ── Hamburger → X ── */
.burger-btn span {
  transform-origin: center;
  transition: transform 0.22s ease, opacity 0.18s ease;
}

.burger-btn.is-open span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}

.burger-btn.is-open span:nth-child(2) {
  opacity: 0;
  transform: scaleX(0);
}

.burger-btn.is-open span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}

/* ── Backdrop ── */
#mobile-nav-backdrop {
  position: fixed;
  inset: 0;
  z-index: 49;
  background: rgba(0, 0, 0, 0.25);
  opacity: 0;
  visibility: hidden;
  transition:
    opacity 0.22s ease,
    visibility 0s linear 0.22s;
}

#mobile-nav-backdrop.is-open {
  opacity: 1;
  visibility: visible;
  transition:
    opacity 0.22s ease,
    visibility 0s linear 0s;
}