JS绝对定位到右下角

<div id="msgBox">
    <div id="msgTitle">最新消息</div>
    <div id="msgContent"><a href="#">这里是内容页面</a></div>
</div>

<style>
    #msgBox{width:150px;border:1px solid silver;background:#C83030;
        position:fixed;right:0px;bottom:250px;
        _position: absolute;//IE兼容性，IE不识别fix
        _top: expression(eval(document.documentElement.scrollBottom+250));
    }
    #msgTitle{height:25px;line-height:25px;color:white;border-bottom:dotted 1px white;text-align:center;}
    #msgContent{height:90px;line-height:25px;color:white;}
    #msgContent a{text-decoration:none;color:white;padding:2px;｝
    #msgContent a:hover{color:#F90;}
</style>