如何在4级下拉菜单中添加滚动条[关闭]

Question

我想在桌面模式下的第二个和第三个下拉菜单中添加更多选项，但列表太长。如何设置 y 轴滚动？

演示

/* Navbar
=================================*/
nav.navbar.bootsnav{
    margin-bottom: 0;
    -moz-border-radius: 0px;
    -webkit-border-radius: 0px;
    -o-border-radius: 0px;
    border-radius: 0px;
    background-color: #fff;
    border: none;
    border-bottom: solid 1px #e0e0e0;
    z-index: 9;
}

nav.navbar.bootsnav ul.nav > li > a{
    color: #6f6f6f;
    background-color: transparent;
    outline: none;
    margin-bottom: -2px;
}

nav.navbar.bootsnav ul.nav li.active > a:hover,
nav.navbar.bootsnav ul.nav li.active > a:focus,
nav.navbar.bootsnav ul.nav li.active > a{
    background-color: transparent;
}

nav.navbar.bootsnav .navbar-toggle{
    background-color: #fff;
    border: none;
    padding: 0;
    font-size: 18px;
    position: relative;
    top: 5px;
}

nav.navbar.bootsnav ul.nav .dropdown-menu .dropdown-menu{
    top: 0;
    left: 100%;
}

nav.navbar.bootsnav ul.nav ul.dropdown-menu > li > a{
    white-space:normal;
}

/* Navbar Responsive
=================================*/
@media (min-width: 1024px) {
    /* General Navbar
    =================================*/
    nav.navbar.bootsnav ul.nav .dropdown-menu .dropdown-menu{
        margin-top: -2px;
    }

    nav.navbar.bootsnav ul.nav.navbar-right .dropdown-menu .dropdown-menu{
        left: -200px;
    }
    
    nav.navbar.bootsnav ul.nav > li > a{
        padding: 30px 15px;
        font-weight: 600;
    }
    
    nav.navbar.bootsnav ul.nav > li.dropdown > a.dropdown-toggle:after{
        font-family: 'FontAwesome';
        content: "\f0d7";
        margin-left: 5px;
        margin-top: 2px;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu{
        -moz-box-shadow: 0px 0px 0px;
        -webkit-box-shadow: 0px 0px 0px;
        -o-box-shadow: 0px 0px 0px;
        box-shadow: 0px 0px 0px;
        -moz-border-radius: 0px;
        -webkit-border-radius: 0px;
        -o-border-radius: 0px;
        border-radius: 0px;
        padding: 0;
        width: 200px;
        background: #fff;
        border: solid 1px #e0e0e0;
        border-top: solid 5px;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu > li a:hover,
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu > li a:hover{
        background-color: transparent;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu > li > a{
        padding: 10px 15px;
        border-bottom: solid 1px #eee;
        color: #6f6f6f;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu > li:last-child > a{
        border-bottom: none;
    }
    
    nav.navbar.bootsnav ul.navbar-right li.dropdown ul.dropdown-menu li a{
        text-align: right;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu li.dropdown > a.dropdown-toggle:before{
        font-family: 'FontAwesome';
        float: right;
        content: "\f105";
        margin-top: 0;
    }
    
    nav.navbar.bootsnav ul.navbar-right li.dropdown ul.dropdown-menu li.dropdown > a.dropdown-toggle:before{
        font-family: 'FontAwesome';
        float: left;
        content: "\f104";
        margin-top: 0;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu ul.dropdown-menu{
        top: -3px;
    }
    
}

@media (max-width: 992px) {
    /* Navbar Responsive
    =================================*/ 
    nav.navbar.bootsnav .navbar-brand    {
        display: inline-block;
        float: none !important;
        margin: 0 !important;
    }
    
    nav.navbar.bootsnav .navbar-header {
        float: none;
        display: block;
        text-align: center;
        padding-left: 30px;
        padding-right: 30px;
    }
    
    nav.navbar.bootsnav .navbar-toggle {
        display: inline-block;
        float: left;
        margin-right: -200px;
        margin-top: 10px;
    }
    
    nav.navbar.bootsnav .navbar-collapse {
        border: none;   
        margin-bottom: 0;
    }

    nav.navbar.bootsnav .navbar-collapse.collapse {
        display: none !important;
    }
    
    nav.navbar.bootsnav .navbar-collapse.collapse.in {
        display: block !important;
    }
    
    nav.navbar.bootsnav .navbar-nav {
        float: none !important;
        padding-left: 30px;
        padding-right: 30px;
        margin: 0px -15px;
    }
    
    nav.navbar.bootsnav .navbar-nav > li {
        float: none;
    }
    
    nav.navbar.bootsnav li.dropdown a.dropdown-toggle:before{
        font-family: 'FontAwesome';
        content: "\f105";
        float: right;
        font-size: 16px;
        margin-left: 10px;
    }
    
    nav.navbar.bootsnav li.dropdown.on > a.dropdown-toggle:before{
        content: "\f107";
    }
    
    nav.navbar.bootsnav .navbar-nav > li > a{
        display: block;
        width: 100%;
        border-bottom: solid 1px #e0e0e0;
        padding: 10px 0;
        border-top: solid 1px #e0e0e0;
        margin-bottom: -1px;
    }
    
    nav.navbar.bootsnav .navbar-nav > li:first-child > a{
        border-top: none;
    }
    
    nav.navbar.bootsnav ul.navbar-nav.navbar-left > li:last-child > ul.dropdown-menu{
        border-bottom: solid 1px #e0e0e0;
    }
    
    nav.navbar.bootsnav ul.nav li.dropdown li a.dropdown-toggle{
        float: none !important;
        position: relative;
        display: block;
        width: 100%;
    }
    
    nav.navbar.bootsnav ul.nav li.dropdown ul.dropdown-menu{
        width: 100%;
        position: relative !important;
        background-color: transparent;
        float: none;
        border: none;
        padding: 0 0 0 15px !important;
        margin: 0 0 -1px 0 !important;
        -moz-box-shadow: 0px 0px 0px;
        -webkit-box-shadow: 0px 0px 0px;
        -o-box-shadow: 0px 0px 0px;
        box-shadow: 0px 0px 0px;
        -moz-border-radius: 0px 0px 0px;
        -webkit-border-radius: 0px 0px 0px;
        -o-border-radius: 0px 0px 0px;
        border-radius: 0px 0px 0px;
    }
    
    nav.navbar.bootsnav ul.nav li.dropdown ul.dropdown-menu  > li > a{
        display: block;
        width: 100%;
        border-bottom: solid 1px #e0e0e0;
        padding: 10px 0;
        color: #6f6f6f;
    }
    
    nav.navbar.bootsnav ul.nav ul.dropdown-menu li a:hover,
    nav.navbar.bootsnav ul.nav ul.dropdown-menu li a:focus{
        background-color: transparent;
    }
    
    nav.navbar.bootsnav ul.nav ul.dropdown-menu ul.dropdown-menu{
        float: none !important;
        left: 0;
        padding: 0 0 0 15px;
        position: relative;
        background: transparent;
        width: 100%;
    }
    
    nav.navbar.bootsnav ul.nav ul.dropdown-menu li.dropdown.on > ul.dropdown-menu{
        display: inline-block;
        margin-top: -10px;
    }
    
    nav.navbar.bootsnav li.dropdown ul.dropdown-menu li.dropdown > a.dropdown-toggle:after{
        display: none;
    }
    
   
    .attr-nav{
        position: absolute;
        right: 60px;
    }
    
    .attr-nav > ul{
        padding: 0;
        margin: 0 -15px -7px 0;
    }
    
    .attr-nav > ul > li > a{
        padding: 16px 15px 15px;
    }
    
    .attr-nav > ul > li.dropdown > a.dropdown-toggle:before{
        display: none;
    }
    
    .attr-nav > ul > li.dropdown ul.dropdown-menu{
        margin-top: 2px;
        margin-left: 55px;
        width: 250px;
        left: -250px;
        border-top: solid 5px;
    }
    
    .top-search .container{
        padding: 0 45px;
    }
    
    /* Mobile Navigation
    =================================*/     
    body > .wrapper{
        -webkit-transition: all 0.3s ease-in-out;
        -moz-transition: all 0.3s ease-in-out;
        -o-transition: all 0.3s ease-in-out;
        -ms-transition: all 0.3s ease-in-out;
        transition: all 0.3s ease-in-out;
    }
}

@media (max-width: 767px) {
    nav.navbar.bootsnav .navbar-header {
        padding-left: 15px;
        padding-right: 15px;
    }
    
    nav.navbar.bootsnav .navbar-nav {
        padding-left: 15px;
        padding-right: 15px;
    }
    }

<link href="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet">
 <link href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.6.3/css/font-awesome.css" rel="stylesheet">

<nav class="navbar navbar-default bootsnav">
        <div class="container">           

            <!-- Start Header Navigation -->
            <div class="navbar-header">
                <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#navbar-menu">
                    <i class="fa fa-bars"></i>
                </button>
                <a class="navbar-brand" href="#brand"><img src="images/brand/logo-black.png" class="logo" alt=""></a>
            </div>
            <!-- End Header Navigation -->

            <!-- Collect the nav links, forms, and other content for toggling -->
            <div class="collapse navbar-collapse" id="navbar-menu">
                <ul class="nav navbar-nav navbar-right" data-in="fadeInDown" data-out="fadeOutUp">
                    <li class="dropdown">
                        <a href="#" class="dropdown-toggle" data-toggle="dropdown" >Dropdowns</a>
                        <ul class="dropdown-menu">
                            <li><a href="#">Custom Menu</a></li>
                            <li><a href="#">Custom Menu</a></li>
                            <li class="dropdown">
                                <a href="#" class="dropdown-toggle" data-toggle="dropdown" >Sub Menu</a>
                                <ul class="dropdown-menu">
                                    <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                     <li><a href="#">Custom Menu</a></li>
                                     <li><a href="#">Custom Menu</a></li>
                                     <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                    <li><a href="#">Custom Menu</a></li>
                                    <li class="dropdown">
                                        <a href="#" class="dropdown-toggle" data-toggle="dropdown" >Sub Menu</a>
                                        <ul class="dropdown-menu">
                                            <li><a href="#">Custom Menu</a></li>
                                            <li><a href="#">Custom Menu</a></li>
                                            <li><a href="#">Custom Menu</a></li>
                                            <li><a href="#">Custom Menu</a></li>
                                        </ul>
                                    </li>
                                    <li><a href="#">Custom Menu</a></li>
                                </ul>
                            </li>
                            <li><a href="#">Custom Menu</a></li>
                            <li><a href="#">Custom Menu</a></li>
                            <li><a href="#">Custom Menu</a></li>
                            <li><a href="#">Custom Menu</a></li>
                        </ul>
                    </li>
                    <li><a href="#">Contact Us</a></li>
                </ul>
            </div><!-- /.navbar-collapse -->
        </div>   

    </nav>
<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.1.0/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/twitter-bootstrap/3.3.7/js/bootstrap.min.js"></script>
<script src="http://demo.htmleaf.com/1704/201704171522/js/bootsnav.js"></script>

我尝试将有关最大高度的CSS添加到下拉列表中。 当我在电脑上浏览网站时，没有出现三级菜单。 如何解决三级菜单不出现的问题？

@media (min-width: 1024px) {
    nav.navbar.bootsnav ul.nav .dropdown-menu .dropdown-menu{
        margin-top: -2px;
        max-height:300px;
        overflow-y:auto
    }
   }

Answer 1

下面给出的代码对于根据引导类创建带有滚动条的下拉菜单非常有用

<<<=html here =>>>

-

<div class="btn-group">
           <button type="button" class="btn btn-default dropdown-toggle" data-toggle="dropdown">
           Scrollable Menu <span class="caret"></span></button>
           <ul class="dropdown-menu scrollable-menu" role="menu">
                           <li><a href="#">Action</a></li>
                           <li><a href="#">Another action</a></li>
                           <li><a href="#">Something else here</a></li>
                           <li><a href="#">Action</a></li>
                           <li><a href="#">Another action</a></li>
                           <li><a href="#">Something else here</a></li>
                           <li><a href="#">Action</a></li>
                           <li><a href="#">Another action</a></li>
                           <li><a href="#">Something else here</a></li>
                           <li><a href="#">Action</a></li>
                           <li><a href="#">Another action</a></li>
                           <li><a href="#">Something else here</a></li>
                           <li><a href="#">Action</a></li>
                           <li><a href="#">Another action</a></li>
                       </ul>
                   </div>
       
       

<<<=css here =>>>

   .scrollable-menu {
       height: auto;
       max-height: 200px;
       overflow-x: hidden;
   }