jQuery is required (if you’re using Bootstrap 3 or 4) 😉
<html> <head> <link rel="stylesheet" href="http://netdna.bootstrapcdn.com/bootstrap/3.1.1/css/bootstrap.min.css"> <!-- THIS LINE --> <script src="//code.jquery.com/jquery-1.11.0.min.js"></script> <script src="http://netdna.bootstrapcdn.com/bootstrap/3.1.1/js/bootstrap.min.js"></script> </head> <body> <div class="panel-group" id="accordion"> <div class="panel panel-default"> <div class="panel-heading"> <h4 class="panel-title"> <a data-toggle="collapse" data-parent="#accordion" href="#collapseOne"> Collapsible Group Item #1 </a> </h4> </div> <div id="collapseOne" class="panel-collapse collapse in"> <div class="panel-body"> Anim pariatur cliche reprehenderit </div> </div> </div> </div> </body> </html>