Designs and documents UI component libraries, design token systems, color palettes, typography scales, spacing systems, and responsive layout frameworks. Produces design specifications, style guides, and developer-ready handoff documentation. Use when a user needs to create a design system, build a component library, define a color palette or typography scale, design UI mockups or wireframes, establish a visual style guide, set up CSS tokens or theming (including dark mode), specify accessible interface components (WCAG AA), or produce layout compositions for web or mobile interfaces.