var str= (navigator.userAgent)

if ((str.indexOf("Safari") > 0)&&(str.indexOf("Windows") == -1))
{
  document.write('<link rel="stylesheet" href="styles5b.css" type="text/css">');
}
else if ((navigator.appName).indexOf("Microsoft")!=-1) {
  document.write('<link rel="stylesheet" href="styles5.css" type="text/css">');
}
else {
  document.write('<link rel="stylesheet" href="styles5a.css" type="text/css">');
}