if (navigator.userAgent.toLowerCase().indexOf('chrome') > -1) {
     var css = document.createElement("link");
     css.rel = "stylesheet";
     css.href = "../css/chrome.css";

     document.getElementsByTagName("head")[0].appendChild(css);
}

if (navigator.userAgent.toLowerCase().indexOf('opera') > -1) {
     var css = document.createElement("link");
     css.rel = "stylesheet";
     css.href = "../css/opera.css";

     document.getElementsByTagName("head")[0].appendChild(css);
}

if (navigator.userAgent.toLowerCase().indexOf('safari') > -1) {
     var css = document.createElement("link");
     css.rel = "stylesheet";
     css.href = "../css/safari.css";

     document.getElementsByTagName("head")[0].appendChild(css);
}

if (navigator.userAgent.toLowerCase().indexOf('mozilla') > -1) {
     var css = document.createElement("link");
     css.rel = "stylesheet";
     css.href = "../css/firefox.css";

     document.getElementsByTagName("head")[0].appendChild(css);
}