Change font size

http://rebuildingsalem.northwestrehab.com/2020/09/11/character/?preview_id=1445&preview_nonce=f1f2dff6c0&_thumbnail_id=-1&preview=true

Above is an example post. I’d like to make the body text larger. I figured out some code, but it only applied to that single line you see at the very top (“I have a confession…”).

I’d rather not put that code for each and every line, would be nice to change the settings to make the default text larger or customizable.

Please advise.