(In reply to Mark Striemer [:mstriemer] from comment #3)
The checkboxes look like you're in "increase contrast" mode in macOS. Is that the case Stanley? Can you provide a screenshot of the preferences page pre-proton with your settings?
As far as the initial bug, I think most in-content pages should've been fixed by bug 1699250, but I still see the new tab page with the pre-proton blue focus colour.
Hey mstriemer -- apologies for the delay.
You are 100% correct; increase contrast on in macOS is turned on and makes it such that Proton does not apply dark-styling to the about:* pages. I've attached an image with that preference turned on and off.