<!-- forum question answer only:

https://www.sitepoint.com/community/t/how-to-make-an-inner-div-height-change-with-outer-div/469156

-->
<div id="divO">divO
  <div id="divI">divI</div>
</div>

#divO {
  background-color: #00589a;
  color: white;
  padding: 10px;
}
#divI {
  position: relative;
  background-color: white;
  margin-top: 40px;
  color: black;
  min-height: 70px;
  max-height: 120px;
  overflow: auto;
}