css-fixed兼容写法

*{background-image:url(about:blank);background-attachment:fixed;}
body{
    background-image:url(about:blank);background-attachment:fixed;
    background-color: #fff;
}

#boxC{
    position: fixed;
    z-index: 999;
    top: 45px;
    right: 0;
    _position:absolute;
    _top:expression(documentElement.scrollTop + 45);
    overflow:hidden; 
    *zoom:1;
}

#boxA{
    position: fixed;
    z-index: 999;
    bottom: 0px;
    left: 0px;
    _position:absolute;
    _top:expression(documentElement.scrollTop + documentElement.clientHeight-this.offsetHeight);
    overflow:hidden; 
    *zoom:1;
}