if(navigator.appVersion.indexOf("Mac") > 1){
    //Mac
    document.write('<link rel="stylesheet" href="/en/common_en/mac.css">')
}
else{
    if(navigator.appName.charAt(0) == "M"){
        //Win IE
        document.write('<link rel="stylesheet" href="/en/common_en/win.css">')
    }
    else{
        //Win NN
        document.write('<link rel="stylesheet" href="/en/common_en/win.css">')
    }
}