Theme Options -> Typography

[paaljoachim]

Customizer: Selecting Custom Body Typography and for instance changing to Sans Serif I can see the change directly.

Custom Headers Typography: Adjusting it to for instance Monospace and Italic the only thing that changes is the Site title. I was expecting that the header menu would be adjusted along with the tagline.

Links decoration (small d) and Header Links Decoration. NB. Change the small d in Links decoration to a capital D.
I selected None but could still see the line below the links. I noticed no visible change when going from None to Underline and back again for both areas.

[aristath]

Custom Headers Typography: Adjusting it to for instance Monospace and Italic the only thing that changes is the Site title. I was expecting that the header menu would be adjusted along with the tagline.

Headers control things like h1, h2, h3 etc. The menus typography is the same as the body typography because semantically they are not headers. By "headers" here we mean actual HTML headers, not the site-header.

Links decoration (small d) and Header Links Decoration. NB. Change the small d in Links decoration to a capital D.
I selected None but could still see the line below the links. I noticed no visible change when going from None to Underline and back again for both areas.

Marked as a bug 👍

[paaljoachim]

Custom Headers Typography could use a tooltip to where one hovers over and it becomes clear what it actually is. It could then say something like affects h1, h2, h3 etc through the full site....