I see, LightBox calculates the width of the shade the wrong way on your theme.
Normally, the output should be like this:
https://vic20reloaded.com/vic-20-cartridge-games-collection-1a/
Anyway, going into bugs of LightView may not be the best way to tackle this. There are themes in which CSS conflicts make too time consuming to fix things.
Since I see you still have those ugly numbers, why don’t you plug in also the FancyBox2 addon – it looks cleaner (no numbers) and might not have conflicts. It simply extends Simplest Gallery and can replace the lightview gallery you are using now.
Trying is simple and take a few clicks, you just download it from here https://www.simplestgallery.com/add-ons/fancybox2/ Install it and set it as the default in Simplest Gallery preferences (or in the page itself)
Let me know if it helped.