How to change or add theme to Android Studio?

You can download new themes from https://github.com/sdvoynikov/color-themes -- note that the project is deprecated at this time, but the sources are still available.

Once you have downloaded the .jar file, go to File -> Import Settings... and choose the file downloaded.

File->Settings->Editor->Colors & Fonts-> In scheme name select Darcula and apply to see a awesome dark background theme editor

Android Studio 3.1.2 File->Settings->Editor->Color Scheme-> In scheme name select Darcula and apply to see a awesome dark background theme editor