Collapse menu gives height problem

I’m working on a navigation where one of the links (called “Gratis”) has an expand option, so that by hovering it, a menu will appear below it. It almost works as desired, however when hovering out of the link “Gratis”, the dark background of the menu suddenly becomes much bigger (before the menu collapses). I’ve tried a lot of things, but I can’t figure out how to solve it. I really appreciate any help!

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