How do I recuce the size of call to action buttons on Stack theme?

Hello there,

Thank you as usual for your terrific support. Could you please tell me how to reduce the overall size of the call to action buttons found on the homepage of This would include the "email address" button in the subscribe area as well as the call to action button which says "Learn more about.." towards the bottom. These call to action buttons also appear on the inner pages as well.

Thanks so much! I'm guessing it would be CSS?