var nome=navigator.userAgent;
brow=nome.search("Mac");

if (brow != -1)  {
   document.write("<LINK REL='stylesheet' HREF='css/mac.css' TYPE='text/css'>"); }
else if (navigator.appName == "Microsoft Internet Explorer") {
   document.write("<LINK REL='stylesheet' HREF='css/pc.css' TYPE='text/css'>"); }
else {
   document.write("<LINK REL='stylesheet' HREF='css/global.css' TYPE='text/css'>"); }