I tried Manjaro GNOME after a long while from Manjaro. But this really throwed me off. The desktop uses Matcha while gdm and the login screen uses Adwaita maia. Why? And I tried to set Matcha to the gdm theme but it is seriously broken.
If the theme is outdated why not use a up to date theme? There are plenty great themes that already have a green variant like Flat Remix, Canta etc.
Moved to feedback section since this does not not seem to be a support request.
Adwaita maia is used in gdm for stability reasons. If you want consistent look, adwaita-maia is included with the default installation and is easy to enable. There is also matching firefox theme included.