bootstrap4 导航栏使用下拉菜单

<nav class="navbar navbar-expand-sm bg-dark navbar-dark"> <!-- Brand --> <a class="navbar-brand" href="#">

Logo</a> <!-- Links --> <ul class="navbar-nav"> <li class="nav-item"> <a class="nav-link" href="#">

Link 1</a> </li> <li class="nav-item"> <a class="nav-link" href="#">

Link 2</a> </li> <!-- Dropdown --> <li class="nav-item dropdown"> <a class="nav-link dropdown-toggle" href="#" id="navbardrop" data-toggle="dropdown"> Dropdown link </a> <div class="dropdown-menu"> <a class="dropdown-item" href="#">

Link 1</a> <a class="dropdown-item" href="#">

Link 2</a> <a class="dropdown-item" href="#">

Link 3</a> </div> </li> </ul></nav>