随滚动条滚动而浮动的层
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.0 Transitional//EN">
<HTML>
<HEAD>
<TITLE> New Document </TITLE>
<Meta NAME="Generator" CONTENT="EditPlus">
<Meta NAME="Author" CONTENT="">
<Meta NAME="Keywords" CONTENT="">
<Meta NAME="Description" CONTENT="">
</HEAD>
<BODY onscroll="javaScript:document.getElementById('buttonDiv').style.posTop=document.body.scrollTop;">
<div id="buttonDiv" style="position:absolute;display:block">
<input type="button" value="button" />
</div>
<script>
document.write(new Array(100).join("<br>"))
</script>
</BODY>
</HTML>