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. Testing Done: Published some updated diffs and saw the "Diff" entry in the change description box looked correct.