Html Bootstrap nav没有崩溃

当我缩小屏幕尺寸时，导航栏项目不会进入切换，它们只是堆叠在导航品牌下.知道为什么吗？

<nav class="navbar navbar-light navbar-expand-md">
        <a class="navbar-brand | logo" href="index.html">Just-Repeat </a>
        <button
          class="navbar-toggler"
          type="button"
          data-bs-toggle="collapse"
          data-bs-target="#collapsibleNavbar"
          aria-controls="navbarToggleExternalContent"
          aria-expanded="false"
          aria-label="Toggle navigation"
        >
          <span class="navbar-toggler-icon"></span>
        </button>

        <div
          class="container-fluid collapse navbar-collapse"
          id="collapsibleNavbar"
        >
      
          <ul class="navbar-nav">
            <li class="navbar-item">
              <a class="navbar-brand" href="indes.html">News </a>
            </li>
            <li class="navbar-item">
              <a class="navbar-brand" href="indes.html">Contact </a>
            </li>
            <li class="navbar-item">
              <a class="navbar-brand" href="indes.html">Privacy </a>
            </li>
          </ul>
        </div>
      </nav>