background-size_html/css

background-image:url(bg.jpg);
background-size:cover;/*等比例拉伸 铺满最短边，长边裁剪*/
background-size:contain;/*铺满最短边，长边空着*/

background-size: 100% 80px;/*横向铺满，纵向80px*/

background-size:150px 80px;/*横向150px，纵向80px*/

background-size:40% 60%;/*横向40%，纵向60%*/

/*Mozilla*/-moz-background-size:auto||||||cover||contain;/*Webkit*/-webkit-background-size:auto||||||cover||contain;/*Presto*/-o-background-size:auto||||||cover||contain;/*W3c*/background-size:auto||||||cover||contain;