Code<html>
<head>
<link href="main.css" rel="stylesheet" type="text/css">
<script>
function aaa(){
left.document.getElementsByTagName("link")[0].href="top.css";
}
</script>
</head>
<body onload="aaa();">
<iframe name="top" src="top.html">
</iframe>
<iframe name="left" src="left.html">
</iframe>
<iframe name="right" src="right.html">
</iframe>
</body>
</html>