Theme Updates Based on Current Site

Good Day

We have a client that makes use of multiple sessions, whereby a session will have a corresponding site. I wanted to Know is there a way to update the theme or color of forms based on the site the user is in within the same company?

Alternatively is there a way to update the sizing of the global options such that the site identifier at the bottom of the form is more visible?

potentially making use of the runtime styler ?