html {
background:url(background.jpg) no-repeat center top;
-webkit-background-size: cover; 
-moz-background-size: cover; 
-ms-background-size: cover; 
-o-background-size: cover; 
background-size: cover;
}

.largeurtotale{
margin-left: auto;
margin-right: auto;
width:80%;
}