Jade is a mod by Snownee, this small pack only changes the Jade GUI to give it a more modern, smooth and minimalistic look. Find the other light or dark versions: New Solid Light Theme for Jade and New Solid Dark Theme for Jade.
Download the correct version for you. Copy the file into the Minecraft installation folder inside "resourcepacks". Enable it by selecting it from the resource packs menu on the game sttings. It should activate when you do this. However, if it does not, open Jade settings (maybe through a Mod Menu mod) and enable it there manually in: Mod Settings/Appearance/Theme.
