源代码 ：
点击运行
<!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/4.3.1/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/1.15.0/umd/popper.min.js"></script> <script src="https://cdn.staticfile.org/twitter-bootstrap/4.3.1/js/bootstrap.min.js"></script> </head> <body> <div class="container"> <h2>按钮中的下拉菜单</h2> <div class="btn-group"> <button type="button" class="btn btn-primary">Primary</button> <button type="button" class="btn btn-primary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown"> <span class="caret"></span> </button> <div class="dropdown-menu"> <a class="dropdown-item" href="#">Link 1</a> <a class="dropdown-item" href="#">Link 2</a> </div> </div> <div class="btn-group"> <button type="button" class="btn btn-secondary">Secondary</button> <button type="button" class="btn btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown"> <span class="caret"></span> </button> <div class="dropdown-menu"> <a class="dropdown-item" href="#">Link 1</a> <a class="dropdown-item" href="#">Link 2</a> </div> </div> <div class="btn-group"> <button type="button" class="btn btn-success">Success</button> <button type="button" class="btn btn-success dropdown-toggle dropdown-toggle-split" data-toggle="dropdown"> <span class="caret"></span> </button> <div class="dropdown-menu"> <a class="dropdown-item" href="#">Link 1</a> <a class="dropdown-item" href="#">Link 2</a> </div> </div> <div class="btn-group"> <button type="button" class="btn btn-info">Info</button> <button type="button" class="btn btn-info dropdown-toggle dropdown-toggle-split" data-toggle="dropdown"> <span class="caret"></span> </button> <div class="dropdown-menu"> <a class="dropdown-item" href="#">Link 1</a> <a class="dropdown-item" href="#">Link 2</a> </div> </div> <div class="btn-group"> <button type="button" class="btn btn-warning">Warning</button> <button type="button" class="btn btn-warning dropdown-toggle dropdown-toggle-split" data-toggle="dropdown"> <span class="caret"></span> </button> <div class="dropdown-menu"> <a class="dropdown-item" href="#">Link 1</a> <a class="dropdown-item" href="#">Link 2</a> </div> </div> <div class="btn-group"> <button type="button" class="btn btn-danger">Danger</button> <button type="button" class="btn btn-danger dropdown-toggle dropdown-toggle-split" data-toggle="dropdown"> <span class="caret"></span> </button> <div class="dropdown-menu"> <a class="dropdown-item" href="#">Link 1</a> <a class="dropdown-item" href="#">Link 2</a> </div> </div> </div> </body> </html>
运行结果