html { 
  margin:0;
  padding:0;
  background: url(datacenter.jpg) no-repeat center fixed; 
  -webkit-background-size: cover; /* pour anciens Chrome et Safari */
  background-size: cover; /* version standardisée */
}
a
{
display:block;
font-family: Arial, Helvetica, sans-serif;
font-size: 20px;
color: black;
text-align:center;
}