CSS3 background-size Property

 background-size: auto|length|cover|contain|initial|inherit;  
 #header  
 {  
   float: right;  
   width: 670px;  
   height: 200px;  
   background-image: url('  ');  
   background-position:center;   
   background-size:cover;  
   background-repeat: no-repeat;  
 }