This gives us a place to disambiguate between implementation statuses
that refer to the entire feature under discussion, and those that just
refer to sub-features.
* Make the font smaller to make them less prominent and help visually
associate the callout with the list.
* Decrease the top margin to more clearly associate them with their
preceding header.
* Lighten the callout background when in another callout to make it
more visible.
* Animate the expand button.