How to increase font size on whole site?

I recently updated the Hiero theme, forgetting that I had globally changed the font size, so that was lost. The main body font is way too small for my preferences, but I can’t figure out how to change it in the CSS. I know very, very little code, by the way.

When I go into “Inspect Element” to fiddle with it, I am able to find a line that pertains to the body font size and change it from 14px to 16px. That fixes the issue on the dummy site, but I can’t find that line in the style editor. The only place where a 14px font size is specified is for the h2. But that’s not what I’m trying to change.

Thanks for any help you’re able to give!