DarkNight was a launch agent that matched Night Shift and the system appearance: however, with the release of macOS Catalina, this feature has now been Sherlocked. As such, DarkNight now just runs a script of your choosing (by default, /usr/local/bin/dark-night, but customizable via defaults write com.saagarjha.DarkNight command /path/to/your/script) whenever the system appearance changes so you can complete the transition. The legacy version of DarkNight, for macOS Mojave and below, is available at the legacy branch.