Field Guide 15: a working starter project and 25 checks that explain each decision in it. A form-associated Lit 3 button reads semantic tokens through the shadow boundary; a Custom Elements Manifest feeds Storybook 10's docs; every story runs as a Vitest browser test with axe as a gate; 12 more tests cover tokens, themes, forms, focus and React 19; a @lit/react wrapper, a server-rendering smoke test and a guard on the static Storybook build complete it. One command, npm run check, runs all of it.
When starting a web component design system or adding Storybook and real-browser tests to an existing Lit library, and you want the seams (forms, focus, tokens, React, production bundles) covered from day one.