Revert "Attempted fix for wonky contributor cards on mobile."

This reverts commit 0ce888e9b428954f1224675f18ed63b5d677fd9e.
Revert "Contributor cards now styled as a true grid."

This reverts commit 85550a52f777f006001bd14baf089dc6a57851fb.
Fixed contributor grid layout on Firefox, IE.
Use backgrounds not shadows to highlight contributors.