<!doctype html>
<title>CSS Test Reference</title>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<style>
  div {
    border: 1px solid;
  }
  #myHeightChanges {
    width: 100px;
    height: 200px;
    background: green;
  }
</style>
<div style="display:flex; flex-direction:column">
  <div style="height:auto">
    <div id="myHeightChanges"></div>
  </div>
</div>