使用btn-xs Bootstrap类创建一个额外的小按钮。您可以尝试运行以下代码来实现btn-xs类：
<!DOCTYPE html> <html> <head> <title>Bootstrap Example</title> <link href = "/bootstrap/css/bootstrap.min.css" rel = "stylesheet"> <script src = "/scripts/jquery.min.js"></script> <script src = "/bootstrap/js/bootstrap.min.js"></script> </head> <body> <div class = "btn-group"> <button type = "button" class = "btn btn-default dropdown-toggle btn-xs" data-toggle = "dropdown"> Subject <span class = "caret"></span> </button> <ul class = "dropdown-menu" role = "menu"> <li><a href = "#">Programming</a></li> <li><a href = "#">Web Dev</a></li> <li><a href = "#">Database</a></li> <li><a href = "#">Networking</a></li> </ul> </div> </body> </html>