How to enable Dark Mode for Xcode

On macOS 10.13 High Sierra and earlier

The Dark Mode is only available on macOS 10.14 Mojave.

On macOS 10.14 Mojave and later

1. On Installation: You'll get asked for the appearance as part of the installation of Mojave.

2. After Installation: If you want to change it afterwards go to System Preferences > General and change the Appearance.

2b. On macOS Catalina: You get even a third option to change the appearance automatically based on your Nightshift preferences.

If you use macOS Mojave (10.14.+), you can enable Dark Mode only for Xcode 10 using this command line.

defaults write com.apple.dt.Xcode NSWindowDarkChocolate -bool true

Workaround:

defaults write com.apple.dt.Xcode _NSSystemAppearanceOverride DarkAppearance

Source (Steve Troughton-Smith's tweet)