WordPress CSS Issue

I wonder if any of you in my “vast” audience are WordPress and/or CSS gurus.

Here’s the deal….

I have this in 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, 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?