Lightbox doesn’t work

Hello,
Lightbox does not open as fullscreen and opens too small somewhere on the screen. The customer can’t use it. I took a look to your demo-site but there is no product that offers a lightbox view. I was hoping to find this function to look how it is ment to be shown.

Can you help and tell me how to set it up?

This is the product where you can check on our staging site: https://dev.langyarnswolle.de/produkt/harmony/

Regards, Clemens