Add CSS for Completion Ribbon:   [#59365552]

https://www.pivotaltracker.com/story/show/59365552
View changes for Completion Ribbon:   [#59365552]

https://www.pivotaltracker.com/story/show/59365552
Small hack to work around interactive state as an 'answer'   [#59365552]

HACK TODO: Clean up the 'answer' question.

https://www.pivotaltracker.com/story/show/59365552