While working on https://jira.greenpeace.org/browse/PLANET-5161 a few other issues with header font weight came up. The font weight in the plastics theme (probably in other themes too) is overriden in many places for different block types. It is unclear which of these rules is working as intended, but according to Will H1, H2 and H3 headings should have 800 font weight, which is not the case currently.

wmorrisj Can you provide the design specifications for the plastics theme?