Inténtalo tú mismo - W3.CSS accordion

<!DOCTYPE html>
<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="/lib/w3.css">

<h2>Accordions</h2>
<p>An accordion with lists:</p>

<div class="w3-accordion w3-card-4">
  <button onclick="myFunction('Demo1')" class="w3-btn-block w3-left-align">
    Accordion 1
  </button>
  <div id="Demo1" class="w3-accordion-content">
    <ul class="w3-ul">
      <li>Jill</li>
      <li>Eve</li>
      <li>Adam</li>
    </ul>  
  </div>
  <button onclick="myFunction('Demo2')" class="w3-btn-block w3-left-align">
    Accordion 2
  </button>
  <div id="Demo2" class="w3-accordion-content">
    <ul class="w3-ul">
      <li class="w3-padding-hor-16">Jill</li>
      <li class="w3-padding-hor-16">Eve</li>
      <li class="w3-padding-hor-16">Adam</li>
    </ul>  
  </div>
</div>

</body>
</html>