header {
  position: sticky;
  top: 0;
  z-index: 1000;
  background: linear-gradient(90deg, rgba(26,31,113,0.95) 0%, rgba(39,48,165,0.95) 100%);
  backdrop-filter: blur(6px);
  box-shadow: 0 4px 12px rgba(0,0,0,0.3);
  transition: background 0.3s ease;
}
header.shrink {
  padding-top: 5px;
  padding-bottom: 5px;
  background: linear-gradient(90deg, #1a1f71 0%, #2730a5 100%);
  box-shadow: 0 3px 10px rgba(0,0,0,0.3);
}

.navbar {
  background: transparent !important;
}

.navbar .nav-link {
  color: #ffffff !important;
  font-weight: 500;
  transition: color 0.3s ease, transform 0.2s;
}

.navbar .nav-link:hover {
  color: #ffd700 !important; /* vàng nhạt nổi bật */
  transform: translateY(-2px);
}

.navbar-brand {
  color: #fff !important;
  font-size: 1.25rem;
  font-weight: 700;
  letter-spacing: 0.5px;
}

.navbar-brand span {
  color: #ffd700; /* tô vàng riêng cho chữ MBX */
}

.navbar-toggler {
  border-color: rgba(255,255,255,0.5);
}