W3Schools Tryit Editor

<!DOCTYPE html>
<html>
<title>W3.CSS</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="4/w3.css">
<body>

<div class="w3-container">
  <h2>Clickable Dropdown</h2>
  <p>Click on the button to open the dropdown menu.</p>
  <div class="w3-dropdown-click">
    <button onclick="myFunction()" class="w3-button w3-black">Click Me!</button>
    <div id="Demo" class="w3-dropdown-content w3-bar-block w3-border">
      <a href="#" class="w3-bar-item w3-button">Link 1</a>
      <a href="#" class="w3-bar-item w3-button">Link 2</a>
      <a href="#" class="w3-bar-item w3-button">Link 3</a>
    </div>
  </div>
</div>

</body>

</html>