The change descriptions for diffs use the same .diff-index class as

the file listing in the diffs. Unfortunately, some of the styles for

that class were moved to the listing's parent container in order to

facilitate the new docking behavior, which caused the look of diff

change descriptions to regress.
This change copies over the few styles we need in order for this to look

correct.

Published some updated diffs and saw the "Diff" entry in the change

description box looked correct.