Constant font size in body text in Sela theme

I have figured out how to change the font size in the Sela theme. But it seems that originally there are different body text sizes on my different pages of my website, so if I change it to 45% for example, because the original font sizes are different, the font sizes on my website pages are different. Is there a way to make sure all the font sizes are the same in the body text across my WordPress site I am self-hosting.
The website I need help with is potentiacoahcing.co.za
Thank you