I always use dark theme. Half of the joplin interface is designed as in the system with a dark theme, but the editor burns the eyes with white color. Please add a dark theme.
Joplin already has multiple dark themes that can be applied with the following instructions: Tools > Options > Appearance > Theme > Select a dark theme > Apply.
If the above doesn't fix your problem, create a Support thread for this issue with all appropriate form fields filled out. Upload an interface screenshot so we can see the issue you're facing. If you're using custom CSS, include it in your issue description.
Edit: The following support request seems like what you are experiencing: All my html notes have white background after v2.14.17
I'm sorry. I haven't fully checked the settings.