[Deff]

<style type="text/css">
.div_one{
 position:relative;
 float:left;
 left:5px;
 background-color:red;
 width:300px;
 height:300px;
 }
</style>

<script type="text/javascript">

var d = document.createElement('div');
 d.className='div_one';
 document.body.appendChild(d);

</script>