Issue with Double Row Bootstrap 4 Navbar - html

Question

I have been trying to create two bootstrap navbars. The first has the website domain name in the center, with a dropdown menu to go to other sections. Then each section has it's own subbar with it's own links.
It currently looks like this.
Which is great and just how I want it. However when I click the dropdown on the brand name, it gets pushed to the left and overlapped with the other navbar.
I also want to bring my theme selector and user profile dropdown to the top nav bar, aligned to the right of the screen. But everytime I try it just ruins the top nav bar and the user profile dropdown gets same overlap issue.
<nav id="topnav" class="navbar navbar-expand-lg navbar-dark bg-primary">
<a class="navbar-brand dropdown-toggle ml-auto mr-auto" href="#navbarDropdown" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">WebsiteName</a>
<div class="dropdown-menu" id="navbarDropdown" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="#">Something else here</a>
</div>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navcollapse" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
</nav>
<nav id ="bottomnav" class="navbar navbar-expand-lg navbar-dark bg-primary py-0 sticky-top">
<div class="container">
<div id="navcollapse" class="collapse navbar-collapse my-2">
<ul class="navbar-nav mr-auto">
<li class="nav-item">
<a class="nav-link" href="/">Section Home</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/Section/">Section</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/Section/">Section</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/Section/">Section</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">
Section Dropdown
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="/Section/">Section</a>
<a class="dropdown-item" href="/Section/">Section</a>
<a class="dropdown-item" href="/Section/">Section</a>
</div>
</li>
</ul>
<ul class="navbar-nav ml-auto">
<li class="nav-item">
<a class="nav-link" href="#" data-toggle="modal" data-target="#themeModal"><i class="fas fa-moon fa-white"></i></a>
<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">
Username
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="/profile/">Profile</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="/section/">section</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="/logout/">Logout</a>
</div>
</li>
</ul>
<form class="form-inline my-2 my-lg-0" action="/search">
<input class="form-control mr-sm-2" type="text" name="q" placeholder="Search">
</form>
</div>
</div>

Answer 1

added
div.dropdown-menu{
left: 50%;
transform: translateX(-50%);
z-index: 9999;
}
to bring it in the center. By default bootstrap has left:0 so t shows at the left side of a.
z-index: 9999 because navbar with sticky-top class has z-index: 1020;
https://codepen.io/Xenio/pen/LqmamQ888
div.dropdown-menu{
left: 50%;
transform: translateX(-50%);
z-index: 9999;
}
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.2.1/css/bootstrap.min.css">
<script src="https://ajax.googleapis.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.6/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.2.1/js/bootstrap.min.js"></script>
<nav id="topnav" class="navbar navbar-expand-lg navbar-dark bg-primary">
<a class="navbar-brand dropdown-toggle ml-auto mr-auto" href="#navbarDropdown" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">WebsiteName</a>
<div class="dropdown-menu" id="navbarDropdown" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="#">Action</a>
<a class="dropdown-item" href="#">Another action</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="#">Something else here</a>
</div>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navcollapse" aria-controls="navbarNav" aria-expanded="false" aria-label="Toggle navigation">
<span class="navbar-toggler-icon"></span>
</button>
</nav>
<nav id ="bottomnav" class="navbar navbar-expand-lg navbar-dark bg-primary py-0 sticky-top">
<div class="container">
<div id="navcollapse" class="collapse navbar-collapse my-2">
<ul class="navbar-nav mr-auto">
<li class="nav-item">
<a class="nav-link" href="/">Section Home</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/Section/">Section</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/Section/">Section</a>
</li>
<li class="nav-item">
<a class="nav-link" href="/Section/">Section</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">
Section Dropdown
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="/Section/">Section</a>
<a class="dropdown-item" href="/Section/">Section</a>
<a class="dropdown-item" href="/Section/">Section</a>
</div>
</li>
</ul>
<ul class="navbar-nav ml-auto">
<li class="nav-item">
<a class="nav-link" href="#" data-toggle="modal" data-target="#themeModal"><i class="fas fa-moon fa-white"></i></a>
<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">
Username
</a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown">
<a class="dropdown-item" href="/profile/">Profile</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="/section/">section</a>
<div class="dropdown-divider"></div>
<a class="dropdown-item" href="/logout/">Logout</a>
</div>
</li>
</ul>
<form class="form-inline my-2 my-lg-0" action="/search">
<input class="form-control mr-sm-2" type="text" name="q" placeholder="Search">
</form>
</div>
</div>