http://www.jeasyuicn.com/css-background-image-stretching.html

background-image:url(bg.png); 
-moz-background-size: 100% 100%; 
-o-background-size: 100% 100%; 
-webkit-background-size: 100% 100%; 
background-size: 100% 100%; 
-moz-border-image: url(bg.png) 0; 
background-repeat:no-repeat\9; 
background-image:none\9; 
filter:progid:DXImageTransform.Microsoft.AlphaImageLoader(src=http://www.mamicode.com/‘bg.png‘, sizingMethod=‘scale‘)/9;