On this website, clicking on the image brings up a lightbox view of the image:
It darkens the main panel on the right, while keeping the navbar normal.
Now on this second site it's a bit messed up, with the navbar only darkened in some areas:
What do I need to change to make the second site act as the first one?
But preferably, how do I make both sites make the whole page dark, including the navbar (bit obviously not the lightbox)?