var agt=navigator.userAgent.toLowerCase();

if (agt.indexOf("opera") != -1)
{
	document.write("<link rel='stylesheet' href='style/opera.css' type='text/css' />"); 
}
else if (agt.indexOf("mozilla") != -1)
{
	document.write("<link rel='stylesheet' href='style/mozilla.css' type='text/css' />"); 
}