Use of different custom fonts in the editor

Hi, I like to use two custom fonts (installed on my server) in the editor.
I checked this Topic (https://villatheme.com/supports/topic/change-font/) with custom CSS code which works okay.
But three things:
1. I like to use another font for the headline. With “td” everything has one font. Is there a way to style a “headline” in a different way?
2. It seems not to work on my mail-app on iPhone. There you see a standard serif font.
3. In the editor I can’t see the custom font in the layout, it’s always Helvetica. Of course, this makes designing difficult.
Any ideas?
Best regards!