SO 47230444

https://stackoverflow.com/questions/47230444/change-style-of-div-with-specific-class/47231570#47231570

by jfcandidofilho

HTML

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.0.0/jquery.min.js"></script>
<div id="menudd" class="show">
  <a href="index.html">Home</a><br />
  <a href="aboutme.html">About Me</a><br />
  <a href="shotterm.html">Short-Term</a><br />
  <a href="middleterm.html">Middle-Term</a><br />
  <a href="longterm.html">Long-Term</a><br />
</div>

CSS

#menudd {
  padding: 0.5em;
  position: fixed;
  overflow: hidden;
  max-height: 0px;
  opacity: 0;
  width: 200px;
  border-radius: 10px;
  box-shadow: 0 0 35px 15px black;
  transition: all 1s ease;
}

#menudd.show {
  opacity: 1;
}

JavaScript

var menu_dropdown = document.getElementById("menudd");
var menu_item = menu_dropdown.getElementsByTagName("A");

menu_dropdown.style.maxHeight = menu_item[0].offsetHeight * menu_item.length + "px";