How to change the font size of the headers

Hallo Sakin, I would like to change the font size of the headers. F.i. I would like to reduce the font size of h2. Maybe I'm overlooking things in the menu, but I suppose that the font size could be adjusted by inserting a line of code in the "Custom CSS Options". If my assumption is corect, could you please supply us with such a line. F.i. h2 with a reduced size to 11 . And if my assumption is wrong, can you please inform about the right way of adjusting the font size? Thank you!