Previously, the font-weight for 500 did not exist in our set, so
all of those examples defaulted to 400. This fixes them to stay
as they previously were by migrating them to a font weight of 400.
This keeps hotspot icons positioned at the front of the message
viewport but behind sidebars (i.e. the left sidebar has a z-index
of 103). Hotspots associated with elements outside of the message
viewport should be individually adjusted at the bottom of hotspots.css.