Overlapping Menu

I’m having trouble finding a solution to an overlapping menu problem for my website

Leaving the page scrolled to the top, click open the first gallery and then open the first image of that gallery. The top menu covers/overlaps this image.

It is fine for galleries that are lower down the page as the top menu scrolls upwards and therefore is not able overlap.

This happens in desktop and is the same issue in both Edge and Chrome.

Anyone with some advice would be much appreciated!

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