title: Stretch div width to match another
body: <p>I have an html layout like the following:</p>
  
  <pre><code>&lt;div id="header"&gt;&lt;/div&gt; 
  &lt;div id="body"&gt;&lt;/div&gt; 
  &lt;div id="footer"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>If the header is a fixed width, how can I force it to stretch to match the width of the body - for cases where the body is wider than the header.</p>