header {
  position: sticky;
  top: 0;
  z-index: 9999;
  transition: background-color 0.3s ease, box-shadow 0.3s ease;
  background-color: transparent;
}

header.navbar-scrolled {
  background-color: #de2d2d;
  box-shadow: 0 2px 12px rgba(0, 0, 0, 0.12);
}