title: Flex elements ignore percent padding in Firefox
body: <p>I'm trying to add padding to an element inside a <code>display:flex</code> element. When the padding is defined as a percent, it doesn't display in Firefox, though it does when defined in <code>px</code>. Both cases work as expected in Chrome.</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-css lang-css prettyprint-override"><code>div {
      background: #233540;
  }
  div &gt; div {
      color: #80A1B6;
  }
  .parent {
      display: flex;
  }
  .padded {
      padding-bottom: 10%;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="parent"&gt;
      &lt;div class="padded"&gt;
          asdf
      &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>Chrome:</p>
  
  <p><a href="https://i.stack.imgur.com/JJG44.png" rel="noreferrer"><img src="https://i.stack.imgur.com/JJG44.png" alt="chrome"></a></p>
  
  <p>Firefox:</p>
  
  <p><a href="https://i.stack.imgur.com/dWruM.png" rel="noreferrer"><img src="https://i.stack.imgur.com/dWruM.png" alt="Firefox"></a></p>
  
  <p><strong>Edit</strong>:
  This may be because of Mozilla's decision to interpret vertical percentages with respect to the height of the parent container. Seems crazy to me. <a href="https://bugzilla.mozilla.org/show_bug.cgi?id=851379" rel="noreferrer">https://bugzilla.mozilla.org/show_bug.cgi?id=851379</a></p>
  
  <p><strong>Edit 2</strong>:
  Yes, it appears that the spec actually defines vertical padding and margin as being resolved against the container's height, so perhaps Chrome is the one not honoring the spec?
  <a href="https://drafts.csswg.org/css-flexbox/#item-margins" rel="noreferrer">https://drafts.csswg.org/css-flexbox/#item-margins</a></p>