html,
body {
  margin: 0;
  overflow: hidden;
  width: 100%;
  height: 100%;
  z-index: inherit;

  background: black;
  background: linear-gradient(to bottom, #000000 0%, #5788fe 100%);
}

.filter {
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  background: #fe5757;
  animation: colorChange 30s ease-in-out infinite;
  animation-fill-mode: both;
  mix-blend-mode: overlay;
}

@keyframes colorChange {
  0%,
  100% {
    opacity: 0;
  }
  50% {
    opacity: 0.9;
  }
}