I want to suggest that this is an awkward behavior. I would expect the revert option to revert the entire style sheet including the style properties contained therein.
I would also expect the .css templates to be an equal alternative to the Style Properties area. But right now you can only revert actual style properties in the Style Properties area. And the .css templates don't necessarily have an indicator that something is customized.
1) Reverting a .css template should revert all style properties that are referenced in that template.
2) If you make changes to the Style Properties area then the associated .css templates should be shown as customized.