Lightbox modal background

In the context of a pull request for XWIKI-21216: Lack of contrast on hover of lightbox buttons when expanded, I propose a solution that would involve a large UI change on the lightbox modal:

When opening Lightbox for an image, a semi transparent modal appears. The color of the background of this modal was hardcoded, and this created some issues with button color on hover:

In order to solve this, I propose to use the panel color scheme in the lightbox modal (instead of hard-coded colors). This has a very noticeable influence on the Iceberg color theme, changing the background of the modal from black to white.

Here are a few pictures to give an idea of the changes proposed:
vv (a) Iceberg theme, before the proposal
vv (b) Iceberg theme, after the proposal
vv (c) Darkly theme, before the proposal
vv (d) Darkly theme, after the proposal

NB: Darkly is a dark color theme, with a basis of a dark grey background with white text.

What do you think of these changes on the Lightbox modal?

Thank you in advance for your feedback! :slight_smile: