With this application you can enable dark mode (avaiable form macOS 10.14 Mojave) in macOS High Sierra.
Use the GUIDE.md file included to learn the Installation Process (realy easy)
Issues
This tool runs some terminal scripts to set the windows color to "Chocolate", this isn't the complete dark mode introduced with Mojave, and not all applications are supported.
HERE'S THE LIST OF THE NOT COMPLETELY SUPPORTED AND NOT SUPPORTED APPLICATIONS. (test made on a mid 2011 Mac Mini with Intel HD Graphics 3000 512 MB and a mid 2010 iMac with an ATI Radeon HD 5750 1024 MB)
Finder - supported except for the AirDrop window and for the items names in the gird view.
All macOS apps with text (Notes, TextEdit, Reminders or script editor) are supported but the text is still black on the same white background.
About This Mac and System Profiler aren't completely supported.
All 3d party apps are still in light mode.
Not all System Preferences prefpanes are supported.
But you can return to "light" mode right from the application macOS High Sierra Dark Mode Patcher.