<!DOCTYPE html>
<html>
   <head>
      <title>Bootstrap Example</title>
      <link rel = "stylesheet" href = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css">
      <script src = "https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
      <script src = "https://maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
   </head>
   <body>
      <h2>Example</h2>
      <div class = "container">
      <div class = "w-50 bg-danger">Danger</div>
      <div class = "bg-primary">Key text!</div>
      </div>
   </body>
</html>