Header navbar with horizontal banner below

With Bootstrap 4.3.1

Code:

<!doctype html>
<html lang="en">
<head>
<meta charset="utf-8">
<title>Bootstrap 4 </title>
<meta http-equiv="X-UA-Compatible" content="IE=edge">
<meta name="viewport" content="width=device-width, initial-scale=1">
<!-- Bootstrap -->
<link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/css/bootstrap.min.css"> 
<style>
body {
padding-top:70px
}
</style>
</head>
<body>
<nav class="navbar fixed-top navbar-expand-lg navbar-dark bg-dark"> <a class="navbar-brand" href="#">Navbar</a>
<button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent1" aria-controls="navbarSupportedContent1" aria-expanded="false" aria-label="Toggle navigation"> <span class="navbar-toggler-icon"></span> </button>
<div class="collapse navbar-collapse" id="navbarSupportedContent1">
<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="#">Link</a> </li>
<li class="nav-item dropdown"> <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown1" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false"> Dropdown </a>
<div class="dropdown-menu" aria-labelledby="navbarDropdown1"> <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>
</li>
<li class="nav-item"> <a class="nav-link disabled" href="#">Disabled</a> </li>
</ul>
<form class="form-inline my-2 my-lg-0">
<input class="form-control mr-sm-2" type="search" placeholder="Search" aria-label="Search">
<button class="btn btn-outline-success my-2 my-sm-0" type="submit">Search</button>
</form>
</div>
</nav>
<div class="container">
<div class="row">
<!--banner image-->
<img src="https://dummyimage.com/1200x400" class="img-fluid" alt="Placeholder image">
</div>
</div>
<!--Supporting scripts. First jQuery, then popper, then Bootstrap JS--> 
<script src="https://code.jquery.com/jquery-3.2.1.min.js" integrity="sha256-hwg4gsxgFZhOsEEamdOYGBf13FyQuiTwlAQgxVSNgt4=" crossorigin="anonymous"></script> 
<script src="https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.7/umd/popper.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/4.3.1/js/bootstrap.min.js"></script>
</body>
</html>