源代码：
左右布局
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 mt-3"> <h3>设置下拉菜单</h3> <p>输入框中添加下拉菜单不需要使用 .dropdown 类。</p> <form> <div class="input-group mt-3 mb-3"> <div class="input-group-prepend"> <button type="button" class="btn btn-outline-secondary dropdown-toggle" data-toggle="dropdown"> 选择网站 </button> <div class="dropdown-menu"> <a class="dropdown-item" href="https://www.google.com">GOOGLE</a> <a class="dropdown-item" href="">RUNOOB</a> <a class="dropdown-item" href="https://www.taobao.com">TAOBAO</a> </div> </div> <input type="text" class="form-control" placeholder="网站地址"> </div> </form> </div> </body> </html>
运行结果