title: width:auto for <input> fields
body: <p>Newbie CSS question. I thought <code>width:auto</code> for a <code>display:block</code> element meant 'fill available space'. However for an <code>&lt;input&gt;</code> element this doesn't seem to be the case. For example:</p>
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="false" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;body&gt;
    &lt;form style='background:red'&gt;
      &lt;input type='text' style='background:green; display:block; width:auto'&gt;
    &lt;/form&gt;
  &lt;/body&gt;</code></pre>
  </div>
  </div>
  </p>
  <p>Two questions then:</p>
  <ol>
  <li><p>Is there a definition of exactly what <code>width:auto</code> does mean? The CSS spec seems vague to me, but maybe I missed the relevant section.</p>
  </li>
  <li><p>Is there a way to achieve my expected behavior for a input field - ie. fill available space like other block level elements do?</p>
  </li>
  </ol>
  <p>Thanks!</p>