Change Body Font Size Throughout?

Hi – I am using the child theme and I’ve tried several ways to change the size of the “body” font / “paragraph” font. I’ve used the editor to add the override style in the child theme in the style.css section. The only thing I notice changing is line height. I’ve tried using % and Pixel height. Can anyone assist? I’d rather change the css than use something like TinyMCE since my client wants a larger paragraph font throughout.

Thanks,