Paragraph font size WordPress 3.8.1

I was trying to change my “article” font size, because it’s too small, but wasn’t able to make any effect. I use the style “paragraph” for my article text, but don’t find where to change it in style.css.

Tried to change the BODY and MAIN font size, but it does no effect.

Could you please tell me where to find it? I have been searching some old tutorials, but the style.css is so different in my version.