javascript - 我刚刚在导航栏中添加了汉堡包按钮，但它现在不起作用？

Question

<nav class="navbar navbar-expand-lg navbar-dark bg-dark ">
    <a class="navbar-brand brand" href="#">Shivaji Maskar</a>
    <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#collapsibleNavbar">
    <div class="collapse navbar-collapse" id="collapsibleNavbar">
      <ul class="navbar-nav ml-auto ">
        <li class="nav-item"><a class="nav-link" href="#">Contact</a></li>
        <li class="nav-item"><a class="nav-link" href="#">Fees</a></li>
        <li class="nav-item"><a class="nav-link" href="#">Item List</a></li>
      </ul>
    </div>

  </nav>

标签： javascripthtmlcssbootstrap-4