Bootscrap NavigationBar 不显示下拉菜单，全屏菜单也没有按预期与标题间隔

Answer 1

你忘了添加

bg-dark

类到导航。代码应该是这样的：

<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
    <div class="container-fluid">
        <a class="navbar-brand" href="">tindog</a>
         <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
        <span class="navbar-toggler-icon"></span>
        </button>
    </div>
 <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <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="">Pricing</a>
        </li>
        <li class="nav-item">
            <a class="nav-link" href="">Download</a>
        </li>
    </ul>
 </div>
</nav>

我将

navbar-brand

包装在一个 div 标签中，其中还有一个名为

container-fluid

的类。 看起来更好