You need to install ElvUI, BenikUI and Addon Skins for this UI to work! (make sure to download the Addons for WoW Classic)
⚫ Installation:
Right now the Download contains an ElvUI Profile in Text format. Just copy and paste it into the Profile window and hit "Import Now". Go to ElvUI -> General and untick Thin Border Theme and you are all set.
⚫ BFA Version:
A Version for Battle for Azeroth can be found HERE