Well it is all CSS driven.
We do provide a ‘quick and dirty’ method of performing a percentage /- on the Options >Styles admin panel. SO – if you think it is too small you could put 110 (for example)… Worth having a play with if you don’t want to actually start changing CSS stylings.

I can use firebug too and try your idea and it's works thanks.

What is the best font-family?

best font family??  wow, hard to answer – very much personal preference…  just find one you like…