Post title and sidebar title font type and size

Hi, I'm really new to creating a website and I've meddled around with the Atahualpa options in order to change to post title font and sidebar font.

However, it seems that when I change the font type in Body, Text and Links, all fonts change together. How can I edit the font on the sidebar independently of the posts and how can I edit the post title's size?

Thank you for your help I appreciate it!