if (navigator.userAgent.indexOf("Opera") != -1) {
    var versionindex = navigator.userAgent.indexOf("Opera") + 6
    if (parseInt(navigator.userAgent.charAt(versionindex)) >= 8) {
        document.write('<link rel="stylesheet" type="text/css" href="' + site_path + 'templates/default/css/opera.css" media="screen" />');
    }
}