

You can use a black theme. Look at gnome-look.org
You can also reverse engineer them to look how they make the theme blank and apply it to adwaita. This is not complicated as themes are mostly CSS.
Edit to add that you can chat with people from open deskttop (gnome look) to ask your question: https://chat.opendesktop.org/#/welcome
Experiment. Apply scientific pro endure for cooking. Just see what people like and what they don’t so you adjust the recipe.