title: How to stretch flex child to fill height of the container?
body: <p>I need to stretch yellow child to fill all height of parent. Without setting parent height. Height of parent should be dependent on blue child text.
      <a href="https://jsfiddle.net/7vaequ1c/1/" rel="noreferrer">https://jsfiddle.net/7vaequ1c/1/</a></p>
  
  <p><div class="snippet" data-lang="js" data-hide="false" data-console="true" data-babel="false">
  <div class="snippet-code">
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div style='display: flex'&gt;
    &lt;div style='background-color: yellow;height: 100%; width: 20px'&gt;
    &lt;/div&gt;
    &lt;div style='background-color: blue'&gt;
    some&lt;br&gt;
    cool&lt;br&gt;
    text
    &lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>