图片显示、PNG透明

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;