Use design tokens instead of hardcoding values

The following discussion from !193170 (merged) should be addressed:

• @ekigbo started a discussion: (+1 comment)

  nitpick: @svedova rather than hardcoding, can we get these values from a design token or some other kind of variable and add to the relevant elements classList rather than directly setting style.backgroundColor? I think the current approach might be a little problematic with dark mode / other colour preferences 🤔

  Happy to be investigated as a follow-up