title: How to stretch children to fill cross-axis?
body: <p>I have a left-right flexbox:</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>.wrapper {
    display: flex;
    flex-direction: row;
    align-items: stretch;
    width: 100%;
    height: 70vh;
    min-height: 325px; 
    max-height:570px; 
  }
  
  .wrapper&gt;.left {
    background: #fcc;
   }
  
  .wrapper&gt;.right {
    background: #ccf;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div class="wrapper"&gt;
    &lt;div class="left"&gt;Left&lt;/div&gt;
    &lt;div class="right"&gt;Right&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  <p>The problem is that the right child is not behaving responsively. To be specific, I want it to fill the height of the wrapper.</p>
  <p>How to accomplish this?</p>