This brings it back a bit closer to the page with the map, so the two
feel cohesive, while still making the selected areas look different to
textboxes.
Gives them some colours, borders and stuff to make them visually
consistent with the rest of Notify.
The idea is the tags and polygons have a similar affordances (i.e.
border thickness, colour) to visually link them and imply that they are
two representations of the same thing.
