引导导航栏与滚动条合拢

我目前正在使用以下CSS代码在930px处折叠导航栏。该代码除了一件事之外效果很好，它没有为更多的导航链接添加滚动条。如何添加滚动条，以便仅当您在下拉列表中滚动时才显示最后的导航链接？请注意，滚动条用于xs屏幕，但不适用于930和768像素之间的屏幕。

的HTML

<!-- Navbar -->
<nav class="navbar navbar-default navbar-fixed-top">
    <div class="container-fluid">
        <!-- Brand and toggle get grouped for better mobile display -->
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#topFixedNavbar1" aria-expanded="false">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a class="navbar-brand" href="#services">Brand</a>
        </div>
        <!-- Collect the nav links, forms, and other content for toggling -->
        <div class="collapse navbar-collapse" id="topFixedNavbar1">
            <ul class="nav navbar-nav navbar-right">
                <li><a href="#carousel1">Welcome</a></li>
                <li><a href="#services">Services</a></li>
                <li><a href="#portfolio">Portfolio</a></li>
                <li><a href="#pricing">Pricing</a></li>
                <li><a href="#about">About</a></li>
                <li><a href="#team-members">Team</a></li>
                <li><a href="#contact">Contact</a></li>
            </ul>
        </div><!-- /.navbar-collapse -->
    </div><!-- /.container-fluid -->
</nav>

的CSS

/*
    Collapse Navbar between 930px and 768px
*/
@media (min-width: 768px) and (max-width: 930px) {
    .navbar-nav .open .dropdown-menu {
        position: static;
        float: none;
        width: auto;
        margin-top: 0;
        background-color: transparent;
        border: 0;
        -webkit-box-shadow: none;
        box-shadow: none;
    }
    .navbar-nav .open .dropdown-menu > li > a {
        line-height: 20px;
    }
    .navbar-nav .open .dropdown-menu > li > a,
    .navbar-nav .open .dropdown-menu .dropdown-header {
        padding: 5px 15px 5px 25px;
    }
    .dropdown-menu > li > a {
        display: block;
        padding: 3px 20px;
        clear: both;
        font-weight: normal;
        line-height: 1.42857143;
        color: #333;
        white-space: nowrap;
    }
    .navbar-header {
        float: none;
    }
    .navbar-toggle {
        display: block;
    }
    .navbar-collapse {
        border-top: 1px solid transparent;
        box-shadow: inset 0 1px 0 rgba(255,255,255,0.1);
    }
    .navbar-collapse.collapse {
        display: none!important;
    }
    .navbar-nav {
        float: none!important;
        /*margin: 7.5px -15px;*/
        margin: 7.5px 50px 7.5px -15px
    }
    .navbar-nav>li {
        float: none;
    }
    .navbar-nav>li>a {
        padding-top: 10px;
        padding-bottom: 10px;
    }
    .navbar-text {
        float: none;
        margin: 15px 0;
    }
    /* since 3.1.0 */
    .navbar-collapse.collapse.in { 
        display: block!important;
    }
    .collapsing {
        overflow: hidden!important;
    }
}

小提琴的例子