[求助 请问怎样让一个div始终位于浏览器窗口的右上角？？？？

<div id="Layer1">
<script>
var lastScrollY=0;
function backtop()
{
diffY=document.body.scrollTop;
percent=.1*(diffY-lastScrollY);
if(percent>0)
{
percent=Math.ceil(percent);
}
else
{
percent=Math.floor(percent);
}
document.getElementById("Layer1").style.pixelTop+=percent;
lastScrollY=lastScrollY+percent;
}
window.setInterval("backtop()",10);
<script>