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<!DOCTYPE html>
<html>
<head>
  <title>Bootstrap 实例</title>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <link rel="stylesheet" href="https://cdn.staticfile.org/twitter-bootstrap/4.1.0/css/bootstrap.min.css">
  <script src="https://cdn.staticfile.org/jquery/3.2.1/jquery.min.js"></script>
  <script src="https://cdn.staticfile.org/popper.js/1.12.5/umd/popper.min.js"></script>
  <script src="https://cdn.staticfile.org/twitter-bootstrap/4.1.0/js/bootstrap.min.js"></script>
</head>
<body>

<div class="container">
  <h2>不同大小的按钮</h2>
  <button type="button" class="btn btn-primary btn-lg">大号按钮</button>
  <button type="button" class="btn btn-primary">默认按钮</button>
  <button type="button" class="btn btn-primary btn-sm">小号按钮</button>
</div>

</body>
</html>
源代码

动行结果
