I'm currently working on a basic webpage and I'm trying to center it using only Bootstrap code (if possible). This is what I have tried so far, but the col-xl-offset-4 doesn't seem to be working.
<script src="https://ajax.googleapis.com/ajax/libs/jquery/1.11.3/jquery.min.js"></script>
<script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>
<link href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css" rel="stylesheet" />
<div class="container">
<div class="jumbotron">
<div class="row vertical-center-row">
<div class="col-xl-6 col-xl-offset-4">
<h1 class="text-primary text-center">Marcell Treville</h1>
<h3 class="text-center"><em>This is a tribute page for the legendary painter "Marcell Treville"</em></h3>
<div class="thumbnail">
<img src="">
<p>this is some text describing the image</p>
<h2>Here's a timeline of Dr. Marcell Treville</h2>
<ul>
<li><strong>1995</strong> item one</li>
<li>item one</li>
<li>item one</li>
<li>item one</li>
<li>item one</li>
<li>item one</li>
</ul>
</div>
</div>
</div>
</div>
</div>