<script>
by a1ex
HTML
<div id="myid">
First
</div>
<script type="text/javascript">
var v=document.createElement('div');
v.setAttribute('class','myclass');
v.textContent='My text';
document.getElementById('myid').appendChild(v);
</script>CSS
#myid {color:#006;}
.myclass {color:#063; background:#adadad;}
script {display:block; color:#F00}