Bootstrap navbar always in mobile state

Hi,
I am wondering if anyone can help me.

I am trying to add a bootstrap navbar to my website, but for some reason, the mobile version is appearing on all versions (desktop, tablet and mobile).

This is the code I am using:

<nav class="navbar navbar-default" role="navigation">
    	  <div class="container">
		    <!-- Brand and toggle get grouped for better mobile display -->
		    <div class="navbar-header">
		      <button type="button" class="navbar-toggle" data-toggle="collapse" data-target="#navbar-brand-centered">
		        <span class="sr-only">Toggle navigation</span>
		        <span class="icon-bar"></span>
		        <span class="icon-bar"></span>
		        <span class="icon-bar"></span>
		      </button>
		      <div class="navbar-brand navbar-brand-centered">Brand</div>
		    </div>

		    <!-- Collect the nav links, forms, and other content for toggling -->
		    <div class="collapse navbar-collapse" id="navbar-brand-centered">
		      <ul class="nav navbar-nav">
		        <li><a href="#">Link</a></li>
		        <li><a href="#">Link</a></li>
		        <li><a href="#">Link</a></li>
		      </ul>
		      <ul class="nav navbar-nav navbar-right">
		        <li><a href="#">Link</a></li>
		        <li><a href="#">Link</a></li>
		        <li><a href="#">Link</a></li>		        
		      </ul>
		    </div><!-- /.navbar-collapse -->
		  </div><!-- /.container-fluid -->
</nav>

@media screen and (min-width:768px){
    .navbar-brand-centered {
        position: absolute;
        left: 50%;
        display: block;
        width: 160px;
        text-align: center;
        background-color: #eee;
    }
    .navbar>.container .navbar-brand-centered, 
    .navbar>.container-fluid .navbar-brand-centered {
        margin-left: -80px;
    }
}

Does anyone know of any reason why this would be?

I am adding Bootstrap via functions.php this way:

function my_scripts() {
    wp_enqueue_style('bootstrap4', 'https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/css/bootstrap.min.css');
    wp_enqueue_script( 'boot1','https://code.jquery.com/jquery-3.3.1.slim.min.js', array( 'jquery' ),'',true );
    wp_enqueue_script( 'boot2','https://cdnjs.cloudflare.com/ajax/libs/popper.js/1.14.3/umd/popper.min.js', array( 'jquery' ),'',true );
    wp_enqueue_script( 'boot3','https://stackpath.bootstrapcdn.com/bootstrap/4.1.1/js/bootstrap.min.js', array( 'jquery' ),'',true );
}
add_action( 'wp_enqueue_scripts', 'my_scripts' );