Site identity and tagline issues

Hi
Can anyone help a newbie pls?
I’m just creating my first WP site using the Masonic theme. I have searched the forum but I can’t find a way to fix the following two problems:
1) Reduce the font size of the Site Title, which I have entered via Site Identity and is too big
2) Reposition the Tagline so that it appears below the Site Title, also entered via Site Identity.
Site Identity doesn’t seem to have any facility to address these issues. Maybe this can be done by Additional CSS or Theme Editor but I’m not experienced in using these.
Any help gratefully accepted!
Thanks, Chas