IMHO, the material design theme for D&D should be just removed. It sucks and makes it all look too sketchy, especially if you browse the forum from your smartphone most of the time.
I would like therefore to ask the group’s opinion in that:
Yes, let’s revert back to the forum’s legacy theme
No, I like this new theme better and would rather keep it as the forum’s default
I set the legacy theme as default now. But please look at the admin panel under Customize. There is another MD theme which I never worked out further: Discourse MD Stock Theme. Maybe you want to work on that one a bit further. The fonts have been imported. That’s the official one from Discourse and you can just import the MD color scheme in that.