if (navigator.platform.indexOf('Mac') > -1) {
    //mac users
    if(navigator.appName.indexOf('Microsoft') > -1){
      //explorer
      document.write('<link href="./img/css/mac.css" rel="styleSheet" type="text/css">');

      }else{
      //netscape
      document.write('<link href="./img/css/mac.css" rel="styleSheet" type="text/css">');

  }

  } else {
    //windows or unix
    if (navigator.appName.indexOf('Microsoft') > -1) {
      //explorer
      document.write('<link href="./img/css/mac.css" rel="styleSheet" type="text/css">');

    } else {
      //netscape
      document.write('<link href="./img/css/win.css" rel="styleSheet" type="text/css">');

    }
  }