.bg {
background-image: url(images/bg.jpg);
background：url(‘../images/bg.jpg‘) no-repeat scroll center 0% 0% transparent;
-webkit-background-size: cover;
-moz-background-size: cover;
-o-background-size: cover;
background-size: cover;
}
原文：http://www.cnblogs.com/ybingbing_1213/p/3935370.html