So Facebook has done it again.

Group banners have changed size and everyone is in a kerfuffle.

I came up with this temp to make things simpler.

The first layer is where you would have your banner that is visable.

The second layer is your border.. now most of this is not visable.. 

just the edge.  I have made mine black but you can edit it however you like.

Here is a preview of how it looks in group 

(blank obviously for this example)

group banner template here