body {
    background-image:
      linear-gradient(45deg, #000 25%, transparent 25%),
      linear-gradient(45deg, transparent 75%, #000 75%),
      linear-gradient(45deg, transparent 75%, #000 75%),
      linear-gradient(45deg, #000 25%, #fff 25%);    

    background-size:100px 100px;       

    background-position:0 0, 0 0, -50px -50px, 50px 50px;
}