Make my WordPress website font size bigger

Here is my website:
https://aerisyuen.com/
I’m using the theme “Adventurous” by “Catch Themes Team”

When I use theme Adventurous 1.0 version, my website font shows larger,
by adding “html { font-size: 70%; }” in style.css last line.

However, after I upgrade theme Adventurous to 1.2, same method cannot make the font size shows larger…

What simple command can be add in style.css, to make whole web site font larger? can anyone help?

Or what method can I downgrade the theme back to Adventurous to 1.0?

Thank you very much.