<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.0.0/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
<a class="navbar-brand" href="#">Mega Dropdown</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 class="collapse navbar-collapse" id="navbarSupportedContent">
<ul class="navbar-nav mr-auto">
<li class="nav-item">
<a class="nav-link" href="#">Link</a>
</li>
<li class="nav-item dropdown">
<a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
Categories
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<div class="container-fluid">
<div class="row">
<nav>
<div class="nav nav-pills flex-column" id="nav-tab" role="tablist">
<a class="nav-item nav-link active" id="nav-home-tab" data-toggle="tab" href="#nav-home" role="tab" aria-controls="nav-home" aria-selected="true">Home</a>
<a class="nav-item nav-link" id="nav-profile-tab" data-toggle="tab" href="#nav-profile" role="tab" aria-controls="nav-profile" aria-selected="false">Profile</a>
<a class="nav-item nav-link" id="nav-contact-tab" data-toggle="tab" href="#nav-contact" role="tab" aria-controls="nav-contact" aria-selected="false">Contact</a>
</div>
</nav>
<div class="tab-content" id="nav-tabContent">
<div class="tab-pane fade show active" id="nav-home" role="tabpanel" aria-labelledby="nav-home-tab">...</div>
<div class="tab-pane fade" id="nav-profile" role="tabpanel" aria-labelledby="nav-profile-tab">...</div>
<div class="tab-pane fade" id="nav-contact" role="tabpanel" aria-labelledby="nav-contact-tab">...</div>