Class CSS being ignored

Here’s the pertinent section from my stylesheet:

.quotes {
	margin-left: auto; margin-right: auto; margin-top: 1em; text-align: center; padding:5px; border: 3px dotted red; background-color: pink;
}

When I use it like this in a post, nothing happens:

<div class="quotes">Choose life</div>

But when I put in all that info as a style like this, it works fine:

<div style="margin-left: auto; margin-right: auto; margin-top: 1em; text-align: center; padding:5px; border: 3px dotted red; background-color: pink">Choose life</div>

Why is the class being ignored in the div?

(I hope this post displays correctly; I miss a preview option!)