css返回顶部图标固定在浏览器右下角且兼容ie6

#e_float{
_position:absolute;
_bottom:auto;
_right:50%;
_margin-right:-536px;
_top:expression(eval(document.documentElement.scrollTop+document.documentElement.clientHeight-this.offsetHeight-(parseInt(this.currentStyle.marginTop,10)||0)-(parseInt(this.currentStyle.marginBottom,10)||0)));
}