Every UI change follows DESIGN.md: its colour tokens, type scale, spacing, components and motion. Colours come only from the tokens, never raw hex or hsl in components. Reuse a pattern listed under Components before writing a new one, and check new UI in every theme the app has.
If a change needs something DESIGN.md does not cover, add it to DESIGN.md in the same change, so the two never disagree.
Conventional Commits: feat:, fix:, docs:, chore:.