Close button invisible on IOS

Hi!
First of all, I have to say that this is a great plugin! It is the only one of many I tried that allowed me to modify the styling as desired by my client.

The following issue I cannot solve however. When I check the mobile menu on an actual iphone, the close button (cross) is invisible. It displays perfectly in Chrome dev tools, so I did not notice it at first.

I’m assuming that it has something to do with missing vendor prefixes for the transform properties, but I’m unable to make the close button visible on my iphone. I cleared cache, used privat mode, the works.

I hope you have an idea what is going wrong?

By the way, the appearance and behaviour of the menu is somewhat modified on the site I’m using it on, but the burger and the close cross should be unaffected by my changes.

Thanks in advance!

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