<link href="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css" rel="stylesheet" id="bootstrap-css">
<script src="//maxcdn.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js"></script>
<script src="//cdnjs.cloudflare.com/ajax/libs/jquery/3.2.1/jquery.min.js"></script>
<!------ Include the above in your HEAD tag ---------->
<div class="container">
<div class="row">
<h2>Create your snippet's HTML, CSS and Javascript in the editor tabs</h2>
</div>
</div>
<?php
//* Do not include the opening php tag.
//* Add logo to admin page
function my_login_logo() { ?>
<style type="text/css">
#login h1 a, .login h1 a {
background-image: url(<?php echo get_stylesheet_directory_uri(); ?>/images/site-login-logo.png);
}
</style>
<?php }
add_action( 'login_enqueue_scripts', 'my_login_logo' );