Custom properties let related rules share a value. They inherit through the document, so a local theme can override an accent without changing the rest of the page. That same mechanism can carry spacing from a fixture into a component. You'll apply one token in more than one place and confirm that the hidden spacing value still works. Transitions need a narrower scope: animate the property you intend to change and give people who prefer reduced motion an override. Keep keyboard focus visible while adding the hover effect. Motion should not become the only signal that an action is available.