Check out example codes for "triangular dropdown in html". It will help you in understanding the concepts better.

Code Example 1

<script src="https://ajax.googleapis.com/ajax/libs/jquery/2.1.1/jquery.min.js"></script>
<ul>
  <li class="dropdown">Dropdown
      <ul class="submenu">
             <li>submenu 1</li>
             <li>submenu 2</li>
      </ul>
</li>
</ul>

Learn ReactJs, React Native from akashmittal.com