Try it Yourself - W3.CSS ref

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

<nav class="w3-dropnav w3-light-grey w3-card-2" style="display:none">
  <div class="w3-container">
  <span onclick="w3_close()" class="w3-closebtn w3-xlarge">�</span>
  </div>  
  <div class="w3-row-padding w3-padding-bottom">
    <div class="w3-third">
    <h3>HTML/CSS</h3>
    <a href="#">Learn HTML</a>
    <a href="#">Learn CSS</a>
    <a href="#">Learn W3.CSS</a>
    </div>
    <div class="w3-third">    
    <h3>JavaScript</h3>
    <a href="#">Learn JavaScript</a>
    <a href="#">Learn jQuery</a>
    <a href="#">Learn AppML</a>
    </div>
    <div class="w3-third">    
    <h3>Graphics</h3>
    <a href="#">Learn Canvas</a>
    <a href="#">Learn SVG</a>
    </div>
  </div>
  <br>
</nav>

</body>
</html>