:root {
  --size: 5vmin;
  background: linear-gradient(#000 50%, #fff 0) 0 0 / 100% var(--size) repeat-y;
  transition: background-size 1s;
  margin: 0;
  min-height: 100vh;
  
  &::before,
  &::after {
    content: "";
    position: absolute;
    width: calc(var(--size) * 5);
    aspect-ratio: 1;
    background: #00f;
    translate: 0 calc(var(--size) * 4);
    transform: translate(-50%, -50%);
    left: 25%;
    top: 50%;
    mix-blend-mode: darken;
  }
  
  &::after {
    translate: 0 calc(var(--size) * -4);
    left: 75%;
    mix-blend-mode: lighten;
  }
  
  &:hover {
    background-size: 0 var(--size);
  }
}