var $agent = navigator.userAgent;

if($agent.match(/Macintosh/) && $agent.match(/Safari/)) {
  document.write("<link rel=\"stylesheet\" type=\"text/css\" media=\"screen\" href=\"fileadmin/css/safari_mac.css\" />");
}

if($agent.match(/Windows/) && $agent.match(/Safari/)) {
  document.write("<link rel=\"stylesheet\" type=\"text/css\" media=\"screen\" href=\"fileadmin/css/safari_win.css\" />");
}