Edit in JSFiddle

body {  
background-color: white;
background-image: linear-gradient( 45deg,black 25%, transparent 25%, transparent 74%, black 75%, black), 
    linear-gradient( 45deg,black 25%, transparent 25%, transparent 74%, black 75%, black);
background-size:100px 100px;
background-position: 0 0, 50px 50px;
}