多张背景图样式

background: 
    url(./static/img/bj_top.png) no-repeat,   
    url(./static/img/bj_bottom.png) 0 100% no-repeat,
    url(./static/img/bj_middle.png) repeat-y;
background-size: 100% auto;
-webkit-background-size: 100% auto;