@keyframes overlay-breathe {
  from {opacity: 0.04;}
  to {opacity: 0.10;}
}
#overlay {
  width: 100%;
  height: 100vh;
  top: 0;
  left: 0;
  position: fixed;

  opacity: 0.10;
  z-index: 1;
  background-image: url('https://ilia.moe/img/noise.gif');
  background-size: 20vmin;

  animation: overlay-breathe 3s ease-in infinite alternate;
}