How to center cards in bootstrap 4?
<p>I am using bootstrap 4 alpha 3.<br>
I want to center the card horizontally in the middle across the page.<br></p>

<p><code>Preview / link:</code> <a href="http://codepen.io/vaibhavsingh97/full/VjRAXW" rel="noreferrer">http://codepen.io/vaibhavsingh97/full/VjRAXW</a></p>

<p>I have tried all the different options listed on the bootstrap 4 example page for cards.</p>

<p>How can I achieve this?</p>