body {
  margin: 0;
  min-height: 100vh;

  background-image: url("grid.png");
  background-repeat: repeat;
  background-size: 900px 900px;
  

  animation: gridScroll 90s linear infinite;
}

@keyframes gridScroll {
  from {
    background-position: 0 0;
  }

  to {
    background-position: 900px 900px;
  }
}