Ey there,
when i create and apply a theme style to a page, the same theme is also applyed to header and footer (that are different templates) and also to template (inserted with the template element). It is intended? It looks like a bug, please check here https://chaosleague.org/miskatonic-university-guida/
You have styled your headings using the Theme Styles exclusively - which is the right approach if you want them to be the same everywhere all across the site.
However, if you create new Theme Styles for a single page and change the fonts for the body and headings, they will naturally apply in the header and footer as well.
As you can see, the selectors (body, h1, h2, h3, …) are identical.
To get around this, you should style your elements in the header and footer more explicitly - either by styling directly on the ID of the respective element or by using a class.