Main menu font carried across to posts

Hi- Installed a font called Impact Label which is a Dymo Label font.

This satisfies the general feel of the site very well, tying into the slider images.

However, In the Main Menu "Appearance" editor the selected font displays as "Vesper Libre"

It is also the default text for admin navigation within the site and for posts.

This isn't ideal. Anything I can do?