Infoboxes now work in dark mode, using a typical dark grey background

and a light grey contrasting outline.
This applies to all the variations of infoboxes. That involved fixing

fade-out gradients on the review request and bug infoboxes, and the Ship

It bar and issue status bar on the review request infoboxes.
The Ship It and issue status areas don't use the same visual flair as on

light mode, instead relegating the responsibility to the icon prefixes

(of which there can be multiple for a given review request anyway).

Tested all the infoboxes with all visual states in light and dark modes.