Unfortunately I had to remove the UnityDecompiled repo due to a request from Unity's legal team.
If you'd like to decompile Unity yourself, find your local UnityEditor.dll and decompile it using either ILSpy or dotPeek
Note that Unity UI is open source. Get it from https://bitbucket.org/Unity-Technologies/ui/
Thanks to the community for all of your contributions over the past three years, it was a great resource while it lasted!
-Matt