No CSS is necessary. Do you want to change it in the layout, or with events?
In the layout view, just click and drag on the rotation handle, just like any other object.
<img src="http://dl.dropbox.com/u/14522925/clickdrag.jpg" border="0" />
As an event, simply change Object.Angle through rotation (relative to current angle) or by setting a specific angle (absolute).