navbar links collapsed and vertically aligned by default

<nav class="navbar navbar-expand-lg navbar-dark indigo">

<!-- Navbar brand -->
 <a class="navbar-brand" href="#">Navbar</a>

<!-- Collapse button -->
 <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>

<!-- Collapsible content -->
 <div class="collapse navbar-collapse" id="navbarSupportedContent">

<!-- Links -->
 <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="#">Features</a>
 </li>
 <li class="nav-item">
 <a class="nav-link" href="#">Pricing</a>
 </li>

<!-- Dropdown -->
 <li class="nav-item dropdown">
 <a class="nav-link dropdown-toggle" id="navbarDropdownMenuLink" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">Dropdown</a>
 <div class="dropdown-menu dropdown-primary" aria-labelledby="navbarDropdownMenuLink">
 <a class="dropdown-item" href="#">Action</a>
 <a class="dropdown-item" href="#">Another action</a>
 <a class="dropdown-item" href="#">Something else here</a>
 </div>
 </li>

</ul>
 <!-- Links -->

<!-- Search form -->
 <form class="form-inline">
 <input class="form-control mr-sm-2" type="text" placeholder="Search" aria-label="Search">
 </form>
 </div>
 <!-- Collapsible content -->

</nav>