.overlay {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background: rgba(0,0,0,0.5);
  backdrop-filter: blur(4px);
  -webkit-backdrop-filter: blur(4px);
  z-index: 999;
  opacity: 0;
  visibility: hidden;
  transition: all var(--transition-slow);
}

.overlay.active {
  opacity: 1;
  visibility: visible;
}