Build screens from the repo's component library instead of hand-rolled markup, and size everything in relative units off one token scale. Use when adding or restyling a button, input, dialog, card, toggle, badge or any control, when writing className, or when the user says shadcn, component library, design tokens, or /ui-components. Do not use for layout, thumb reach and keyboard paths (mobile-a11y), browser tests (ui-verify), or TypeScript taste (code-quality-standards).
