I have a problem with the menu on mobile: http://blomstra.de/about/
On dektop it works all good, but on mobile the menu background suddenly expands when scrolling down.
This is how it is supposed to look, menu backgorund is just big enough to cover the menu
(top of the page)
If I start scrolling down this happens:
Menu background suddenly expands and covers way more than it should.
How can I fix this?
All the best & thanks for your help,