Difference between BundleConfig.cs and Bundle.Config

Hi Folks,
Just wondering what the difference is between using BundleConfig.cs and Bundle.Config.
I was trying to add a StyleBundle to my Asp.Net 5 forms application and kept getting a script error for each css file in the budle (on the first piece of css in the file).  I see there are no SyleBundles in the BundleConfig.cs file any more and there is a new Bundle.Config, but cant find any documentation on how these now work.