Change headings site-wide

I am new to twenty twenty three.
I cannot find a way to change the size of the H2 and H3 headings size site-wide.
Also no documentation or topic in the forums about this.
Is there a way to change the size of all the headings (eg H2) at once?
Or is the only way to do that on every single page?

The page I need help with: [log in to see the link]