title: How to indent multiple levels of select optgroup with CSS?
body: <p>Just trying to indent optgroup blocks by nesting depth really, I've tried a general <code>margin-left</code> rule, nested elements then trying to apply the same rule, tried <code>padding-left</code>... is indenting like this possible? It seems elementary :P</p>
  
  <p>In the example below, the optgroup labelled 'client2_a' should be indented more than the others, because it is nested inside 'client2'.</p>
  
  <p><a href="http://jsfiddle.net/Tb5Rc/5/" rel="noreferrer">http://jsfiddle.net/Tb5Rc/5/</a></p>