Css 使用Bootstrap 4将中等屏幕的搜索栏移到第二行

此导航栏使用引导4。对于中等屏幕（768px到991px），我希望搜索栏和按钮移动到第二行，因为它在大屏幕和更高屏幕上。目前，在中等屏幕上，搜索栏在其他导航链接旁边挤压：

它在大屏幕/超大屏幕上的外观：

根据首次回答建议更新代码：

<nav class="navbar navbar-expand-md navbar-fixed-top navbar-dark bg-navbar">
    <div class="container">
        <a class="navbar-brand" href="/" style="align-children: middle">
        <span class="" aria-hidden="true"></span>
            Example
        </a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#site-nav" aria-expanded="false" aria-label="Toggle navigation">
            <span class="sr-only">Toggle navigation</span>
            <span class="navbar-toggler-icon"></span>
        </button>

        <div class="collapse navbar-collapse ml-auto" id="site-nav">
            <ul class="navbar-nav mr-auto">
                <li class="nav-item active">
                    <a class="nav-link" href="/">Home
                        <span class="sr-only">(current)</span>
                    </a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/agencies/">Agencies</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/meetings/">Meetings</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/agenda/">Agenda</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/documents/">Documents</a>
                </li>
            </ul>
            <form class="form-inline mt-3 mb-3" role="search" action="/search/" method="post">
                <div class="btn-group">
                    <input type="text" name="request" class="form-control" placeholder="Search Documents">
                    <button type="submit" class="btn search-button">Search</button>
                </div>
            </form>
        </div>
    </div>
</nav>

切换导航












搜寻

将搜索表单的内容放在一个

btn组中

，该组应将它们放在一起：

        <form class="form-inline mt-3 mb-3" role="search" action="/search/" method="post">
            <div class="btn-group" role="group" aria-label="Basic example">
                <input type="text" name="request" class="form-control" placeholder="Search Documents">
                <button type="submit" class="btn search-button">Search</button>
            </div>
        </form>

搜寻

您可以使用响应型flexbox方向UTIL。例如，

导航栏折叠上的
flex column flex xl row

<nav class="navbar navbar-expand-md fixed-top navbar-dark bg-dark">
    <div class="container">
        <a class="navbar-brand" href="/" style="align-children: middle">
        <span class="" aria-hidden="true"></span>
            Example
        </a>
        <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#site-nav" aria-expanded="false" aria-label="Toggle navigation">
            <span class="sr-only">Toggle navigation</span>
            <span class="navbar-toggler-icon"></span>
        </button>

        <div class="collapse navbar-collapse ml-auto align-items-start align-items-xl-center flex-column flex-xl-row" id="site-nav">
            <ul class="navbar-nav mr-auto">
                <li class="nav-item active">
                    <a class="nav-link" href="/">Home
                        <span class="sr-only">(current)</span>
                    </a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/agencies/">Agencies</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/meetings/">Meetings</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/agenda/">Agenda</a>
                </li>
                <li class="nav-item">
                    <a class="nav-link" href="/documents/">Documents</a>
                </li>
            </ul>
            <form class="form-inline ml-2" role="search" action="/search/" method="post">
                <div class="form-group">
                    <input type="text" name="request" class="form-control" placeholder="Search Documents">
                </div>
                <button type="submit" class="btn search-button">Search</button>
            </form>
        </div>
    </div>
</nav>


切换导航












搜寻


注意：您使用的是
navbar expand md
，因此navbar将折叠到sm上的切换器中。如果您想在
md
上显示堆叠菜单/表单，则应将导航栏缩小到
sm

另请参见：
我认为您的意思是“您应该将导航栏扩展到lg”（在中屏幕上显示切换器）