var st = document.styleSheets;
var accP = navigator.userAgent.toUpperCase();

if(accP.indexOf("WIN") >= 0) accName ="win";
else if(accP.indexOf("MAC") >= 0) accName ="mac";
else accName ="nor";

if(st){ for (var i = 0; i < st.length; i++){
if(accName && (st[i].title == accName || st[i].title == ""))
st[i].disabled = false;
else st[i].disabled = true}
}