<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap Example</title>
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/css/bootstrap.min.css">
  <script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
  <script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.1.3/js/bootstrap.min.js"></script>
</head>
<body>

<div class="container">
  <h2>Dropdowns</h2>                                        
  <div class="dropdown">
    <button type="button" class="btn btn-primary dropdown-toggle" data-toggle="dropdown">
      Dropdown button
    </button>
    <div class="dropdown-menu">
      <a class="dropdown-item" href="#">Link 1</a>
      <a class="dropdown-item" href="#">Link 2</a>
      <a class="dropdown-item" href="#">Link 3</a>
    </div>
  </div>
</div>

</body>
</html>

External CSS

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External JavaScript

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