var usra = navigator.userAgent;
var osMac = (usra.indexOf("Mac") != -1)?true:false;

if(osMac){
	document.write('<LINK rel="stylesheet" href="css/mac.css" type="text/css">'); // mac
}else{
	document.write('<LINK rel="stylesheet" href="css/win.css" type="text/css">'); // win,other
}