body {
  background-color: #eee;
  background-image: 
    linear-gradient(45deg, #ccc 25%, transparent 25%), 
    linear-gradient(-45deg, #ccc 25%, transparent 25%), 
    linear-gradient(45deg, transparent 75%, #ccc 75%), 
    linear-gradient(-45deg, transparent 75%, #ccc 75%);
  background-size: 20px 20px;
  background-position: 0 0, 0 10px, 10px -10px, -10px 0px;
}