title: CSS for "fill parent width?"
body: <p>I have an item on the DOM that I'd simply like to have fill its parent's width, regardless of what that is:</p>
  
  <pre><code>&lt;div width="800"&gt;
      &lt;div class="filler"&gt;&lt;/div&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>How can I specify in CSS that the <code>filler</code> class match the width of its parent?</p>
  
  <pre><code>.filler {
      ?
  }
  </code></pre>