ellend5 on "twenty eleven theme h1, h2 tags don't work"

I am building 2 sites; one with twenty eleven theme and the other on twenty twelve. On the twenty eleven, I have the Twenty Eleven Theme Extensions plugin and I believe that bypasses building a child theme. I am happy to see you can put any CSS customizations right there.

I CANNOT figure out where to make changes to the H1 and H2 tags. They only make the font bold; font is the same size as the regular text on the pages. Twenty twelve has different font sizes with H1 thru H6 tags.

My question is this: What is the proper code that I can put on the theme extensions plugin to make H1 and H2 tags perform just like on the twenty twelve theme?

thanks in advance for any advice!