title: How to force child div to be 100% of parent div's height without specifying parent's height?
body: <p>I have a site with the following structure:</p>
  
  <pre><code>&lt;div id="header"&gt;&lt;/div&gt;
  
  &lt;div id="main"&gt;
    &lt;div id="navigation"&gt;&lt;/div&gt;
    &lt;div id="content"&gt;&lt;/div&gt;
  &lt;/div&gt;
  
  &lt;div id="footer"&gt;&lt;/div&gt;
  </code></pre>
  
  <p>The navigation is on the left and the content div is on the right. The information for the content div is pulled in through PHP, so it's different every time.</p>
  
  <p>How can I scale the navigation vertically so that its height is the same as the content div's height, no matter which page is loaded?</p>