I have exportet all from GeneratePress in website A and imported this into the new website B.
In the Website A everything with the submenus is OK, in the website B the colours of submenus are different if the main menu item is selected and not as nice as in the website A and the hover is not running.
Website A:
https://www.simon-weber.de/team/
Website B:
http://wp.fritz-simon.de/publikationsverzeichnis/
Thank you for some hints!