body{    background-image:url(about:blank); background-attachment:fixed;  /*ie 防抖动*/}.fix_to_top {   _position:absolute; _top:expression(eval(document.documentElement.scrollTop));  }.fix_to_bottom{	top: expression(eval((document.compatMode&&document.compatMode=="CSS1Compat")?documentElement.scrollTop+documentElement.clientHeight-this.clientHeight-1:document.body.scrollTop+document.body.clientHeight-this.clientHeight-1));}