How to change the Spyder editor background to dark?
If you're using Spyder 3, please go to
Tools > Preferences > Syntax Coloring
and select there the dark theme you want to use.
In Spyder 4, a dark theme is used by default. But if you want to select a different theme you can go to
Tools > Preferences > Appearance > Syntax highlighting theme
Tools->Preferences->Syntax coloring->Scheme changed to "Spyder Dark"