导航栏在响应模式下未关闭
所有已添加的库都已准备好 ''''
<div class="collapse navbar-collapse justify-content-end" id="navbarSupportedContent">
<ul class="navbar-nav mb-2 mb-lg-0">
<li class="nav-item active">
<select class="users" id="users">
<option><a class="nav-link active" href="#">User</a></option>
<option><a class="nav-link active" href="#">Employee</a></option>
<option><a class="nav-link active" href="#">Admin</a></option>
</select>
</li>
</ul>
</div>
</div>
</nav>
```` 
我已经删除了
<div class="collapse navbar-collapse justify-content-end" id="navbarSupportedContent">部分，现在您可以在更改分辨率时看到下拉菜单。