bootstrap 导航条,在 google chrome 出现的问题

做出来本应该是横着的我做出来的导航条是竖着的，本来以为是自己代码写错了。然后换官方的试，但还是出现了相应的问题 如下图官方给出的结果 我的为什么是竖着的？？？

我的代码

'''ruby

<button aria-expanded="false" class="navbar-toggle collapsed" data-target="#bs-example-navbar-collapse-1" data-toggle="collapse" type="button"> Toggle navigation </button> Brand

    <!-- Collect the nav links, forms, and other content for toggling -->
    <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
        <ul class="nav navbar-nav">
            <li class="active"><a href="#">Link <span class="sr-only">(current)</span></a></li>
            <li><a href="#">Link</a></li>
            <li class="dropdown">
                <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
                <ul class="dropdown-menu">
                    <li><a href="#">Action</a></li>
                    <li><a href="#">Another action</a></li>
                    <li><a href="#">Something else here</a></li>
                    <li role="separator" class="divider"></li>
                    <li><a href="#">Separated link</a></li>
                    <li role="separator" class="divider"></li>
                    <li><a href="#">One more separated link</a></li>
                </ul>
            </li>
        </ul>
        <form class="navbar-form navbar-left">
            <div class="form-group">
                <input type="text" class="form-control" placeholder="Search">
            </div>
            <button type="submit" class="btn btn-default">Submit</button>
        </form>
        <ul class="nav navbar-nav navbar-right">
            <li><a href="#">Link</a></li>
            <li class="dropdown">
                <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Dropdown <span class="caret"></span></a>
                <ul class="dropdown-menu">
                    <li><a href="#">Action</a></li>
                    <li><a href="#">Another action</a></li>
                    <li><a href="#">Something else here</a></li>
                    <li role="separator" class="divider"></li>
                    <li><a href="#">Separated link</a></li>
                </ul>
            </li>
        </ul>
    </div><!-- /.navbar-collapse -->
</div><!-- /.container-fluid -->

</nav> ''' **官方地址** https://v3.bootcss.com/components/#navbar 进入选导航条，就可看到代码