Wrap you page content in a container to bring the content in tighter and center align in the page. The max-width on the container is 600px which is the standard width for emails. It will be responsive on mobile devices.
<div class="container"> <!-- Content here --> </div>
A fluid container is unlike a container in that it doesn’t have it’s max-width set. It does however still have padding on the edges to give the content better spacing towards the edge of the email.
<div class="container-fluid"> <!-- Content here --> </div>