Дописать стили после получения ответа

[nemo]

<script type="text/javascript" language="javascript">
var req=Create();
function id(id)
{return document.getElementById(id);}
function Create(){
if(navigator.appName == "Microsoft Internet Explorer"){
req=new ActiveXObject("Microsoft.XMLHTTP");
}else{
req=new XMLHttpRequest();}
return req;}
function Request(query)
{req.open('post','ajax.php',true);
req.onreadystatechange=Refresh;
req.setRequestHeader("Content-Type","application/x-www-form-urlencoded;charset=utf-8");
req.send(query);}
function Refresh()
{if(req.readyState==4)
id('ajax_final_load').innerHTML=req.responseText;
else
id('ajax_loading').innerHTML='загрузка';}
function Pusk()
{var query;
query='txt='+encodeURIComponent(id('ajax_load').value);
Request(query);}
</script>

плз как дописать после получения ответа т.е
{if(req.readyState==4)

это
<style type="text/css">
</style

[subzey]

var myStyle = document.createElement("style");
myStyle.type = "text/css";
myStyle.innerHTML = "\
#my-div, #my-div * {\
color: red;\
}\
";
document.getElementsByTagName("head")[0].appendChild(myStyle);