UX: Improve positioning of controls in lightboxes (PR #13108)

This PR fixes an issue where controls scroll in lightboxes with large images (after zooming in)

Before:

Notice how controls like the close button, the next and previous button, and the image metadata also scroll? This is an undesired behavior.

After:

This is the desired behavior; only the image should scroll.

The changes in this PR apply to both desktop and mobile.

GitHub