How to make flexbox child's height to fit to content instead of 100% height of its container
<p><div class="snippet" data-lang="js" data-hide="false">
<div class="snippet-code">
<pre class="snippet-code-css lang-css prettyprint-override"><code>#container {
  display:flex;
  height:300px;
  background:#333;
}
#child1 {
  width:30%;
  background:#3cf;
}
#child2 {
  width:30%;
  background:#3fc;
}
#child3 {
  width:40%;
  background:#cf3;
}
#child1_child {
  width:100%;
  background:#fc3;
}
pre {
  margin:0px;
}</code></pre>
<pre class="snippet-code-html lang-html prettyprint-override"><code>    &lt;div id="container"&gt;
    &lt;div id="child1"&gt;&lt;div id="child1_child"&gt;&lt;pre&gt;CONTENT&lt;BR&gt;CONTENT&lt;BR&gt;CONTENT&lt;BR&gt;CONTENT&lt;/pre&gt;&lt;/div&gt;&lt;/div&gt;
    &lt;div id="child2"&gt;&lt;/div&gt;
    &lt;div id="child3"&gt;&lt;/div&gt;
    &lt;/div&gt;</code></pre>
</div>
</div>
</p>

<p>The height of <code>#child1</code> is automatically set to the same height of <code>#container</code>, How can I make it to fit to <code>#child1_child</code> rather than 100% height of <code>#container</code>?</p>

<p>The height of <code>#child1_child</code> is not static, it can be changed by content inside of it, height of <code>#child1</code> with static value is useless.</p>