css:

margin:0px auto;   自动居中display:block;　　　块显示，图片自动伸缩width: 400px;height: 400px; 透明 示例：

width: 325px;    height: 378px;    display: block;　　 position: absolute;    top: 0px;    bottom: 0px;    right: 0px;    z-index: 100;    margin: auto 0px auto 0px;    opacity:0.9;     -moz-opacity:0.9;    -khtml-opacity:0.9;    background-image: url(../../../_bg.png);    background-position: left center;    background-repeat: no-repeat;