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" style="text-align:center;"> <h2>下拉菜单</h2> <p> .dropleft 类用于设置下拉菜单向左弹出：</p><br> <!-- Default dropleft button --> <div class="btn-group dropleft"> <button type="button" class="btn btn-secondary dropdown-toggle" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"> Dropleft </button> <div class="dropdown-menu"> <!-- Dropdown menu links --> <a class="dropdown-item" href="#">Action</a> <a class="dropdown-item" href="#">Another action</a> <a class="dropdown-item" href="#">Something else here</a> <div class="dropdown-divider"></div> <a class="dropdown-item" href="#">Separated link</a> </div> </div> <br><br><br> <!-- Split dropleft button --> <div class="btn-group dropleft"> <button type="button" class="btn btn-secondary"> Split dropleft </button> <button type="button" class="btn btn-secondary dropdown-toggle dropdown-toggle-split" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"> <span class="sr-only">Toggle Dropleft</span> </button> <div class="dropdown-menu"> <!-- Dropdown menu links --> <a class="dropdown-item" href="#">Action</a> <a class="dropdown-item" href="#">Another action</a> <a class="dropdown-item" href="#">Something else here</a> <div class="dropdown-divider"></div> <a class="dropdown-item" href="#">Separated link</a> </div> </div> </div> </body> </html>
运行结果