title: align-content not working on flex items
body: <p>I have a row-direction flexbox nested in a column-direction flexbox, but when I want to use <code>align-content</code> in the child, it doesn't work.</p>
  
  <p>When I replace <code>display:flex</code> of the parent by a <code>display:block</code>, it works.</p>
  
  <p>In the code below, we can see that <code>.row</code> <code>align-content: flex-end;</code> doesn't work. But if I replace the <code>.column</code> <code>display: flex;</code> with <code>display: block;</code>, the <code>align-content: flex-end;</code> works.</p>
  
  <p>Is it possible to fix this, please?</p>
  
  <p><div class="snippet" data-lang="js" data-hide="false">
  <div class="snippet-code">
  <pre class="snippet-code-css lang-css prettyprint-override"><code>body {
      background-color: grey;
  }
  
  .column {
      display: flex;
      flex-flow: column nowrap;
      justify-content: flex-start;
      align-items: stretch;
      background-color: green;
  }
  
  .row {
      display: flex;
      flex-flow: row wrap;
      justify-content: space-around;
      align-content: flex-end;
      align-items: center;
      background-color: red;
  }
  
  .row-test {
      min-height: 200px;
  }
  
  span {
      width: 30%;
      background-color: orange;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;body class="column"&gt;
      &lt;section class="row row-test"&gt;
          &lt;span&gt;Test Test Test Test Test Test Test Test Test&lt;/span&gt;
          &lt;span&gt;Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test Test&lt;/span&gt;
      &lt;/section&gt;
  &lt;/body&gt;</code></pre>
  </div>
  </div>
  </p>