title: z-indexing floating divs
body: <p>I have two divs float:left. I z-index the first div to be above, but it doesn't work. Is this because floated elements are not positioned?</p>
  
  <pre><code>&lt;html&gt;
  
  &lt;style&gt;
      #wrap{
          background:#666;
      }
  
      #menu, #thumbs{
          float:left;
      }
  
      #menu{
          background:#06C;
          z-index:10;
      }
      #thumbs{
          background:#0CF;
          margin-left:-20px;
      }
  
  &lt;/style&gt;
  &lt;/head&gt;
  
  &lt;body&gt;
  
  &lt;div id="wrap"&gt;
      &lt;div id="menu"&gt;
      &lt;p&gt;menu&lt;/p&gt;
      &lt;/div&gt;
      &lt;div id="thumbs"&gt;
      &lt;p&gt;thumbs&lt;/p&gt;
      &lt;/div&gt;
  &lt;/div&gt;
  
  
  &lt;/body&gt;
  &lt;/html&gt;
  </code></pre>