cssでの演算

.mycss{
	position:fixed;
	bottom:10px;
	margin-left:7px;
	_position:absolute;
	_top:expression(eval(document.documentElement.scrollTop+document.documentElement.clientHeight - 120));
	width:22px;
	height:59px;
	background:url(images/backtop.gif) no-repeat;
	cursor:pointer;
}