Mobile menu showing incorrectly

He people,

I’m fixing a website for the client of a friend. It’s an old website that has rarely done any updates. Updating everything wasn’t even possible, a server error showed up. We decided to do the bare minimum so they can start advertising on social media and we’ll build completely new website later.

We do however, need to fix one issue. If you open the mobile menu on this website, it shows up with a white background and white text. The links to the other pages are clickable, but I can’t see them.

I tried custom CSS, a mobile menu plugin and deactivating other plugins. But nothing has worked so far, does anyone have a solution?

The page I need help with: [log in to see the link]