title: css columns: use available width
body: <p>Anyone know a way to make it so that when the menu div is omitted, the main div uses all the available width? </p>
  
  <pre><code>    +-------------- container -------------+
      |  +--- menu ---+  +---- main ------+  |
      |  |            |  |                |  |
      |  |            |  |                |  |
      |  +------------+  +----------------+  |
      +--------------------------------------+
  
  
  
      +-------------- container -------------+
      |  +------------- main -------------+  |
      |  |                                |  |
      |  |                                |  |
      |  +--------------------------------+  |
      +--------------------------------------+
  </code></pre>