title: Flexbox: Div height dependent to sibling div
body: <p>I got two div's wrapped inside a wrapper, both have dynamic heights:</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-css lang-css prettyprint-override"><code>#wrapper {
    display: flex;
  }</code></pre>
  <pre class="snippet-code-html lang-html prettyprint-override"><code>&lt;div id="wrapper"&gt;
    &lt;div id="left"&gt;dynamic content, height could be more or less than #right&lt;/div&gt;
    &lt;div id="right"&gt;dynamic content, height could be more or less than #left&lt;/div&gt;
  &lt;/div&gt;</code></pre>
  </div>
  </div>
  </p>
  
  <p>The left div should always be the leading factor for the wrappers height. Is there a way to do this pure by css alone?</p>
  
  <p>The width of the columns is known, I'm using Bootstrap grid layout.</p>
  
  <p>I know by giving the <code>#wrapper</code> div <code>display: flex</code> the children div's are equal of height. Is there some property to tell the browser <code>#left</code> height is always the <code>wrapper</code>'s height , no matter if the content is more of less than <code>#right</code>? I've been going through <a href="https://css-tricks.com/snippets/css/a-guide-to-flexbox/" rel="nofollow noreferrer">the Complete Guide to Flexbox</a>, but such property seems not to exist.</p>
  
  <hr>
  
  <p>Here a picture to make my question clearer:</p>
  
  <p><a href="https://i.stack.imgur.com/bmDUI.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bmDUI.png" alt="Explanation"></a></p>