var str= (navigator.userAgent)

if ((str.indexOf("Safari") > 0)&&(str.indexOf("Windows") == -1))
{
  document.write('<link rel="stylesheet" href="styles7b.css" type="text/css">');
}

else if ((navigator.appName).indexOf("Microsoft")!=-1)
{
  document.write('<link rel="stylesheet" href="styles7.css" type="text/css">');
}

else
{
  document.write('<link rel="stylesheet" href="styles7a.css" type="text/css">');
}