Colour palette with semantic aliases (primary, surface, error, success) built on a two-tier token architecture: primitive tokens define the raw values (--color-red-500: #ef4444) and semantic tokens map purposes to primitives (--color-surface-danger: var(--color-red-500)) -- so changing "danger" from red to another colour requires changing one semantic token, not updating hundreds of hardcoded hex values across the codebase. Style Dictionary as the token definition format: tokens defined once in JSON, exported by the build pipeline to CSS custom properties, Tailwind v4 @theme block, React Native StyleSheet values, Figma Tokens Plugin format, and iOS/Android native colour definitions -- ensuring design and code are always reading from the same source. Typographic scale defined with named purpose roles (Display, Heading 1-4, Body Large, Body, Caption, Label) rather than arbitrary size values, each role specifying font-family, font-weight, font-size, line-height, and letter-spacing -- so a designer using "Heading 2" and a developer applying className="heading-2" are referencing identical computed styles. Spacing scale on a geometric or arithmetic progression (4px, 8px, 12px, 16px, 24px, 32px, 48px, 64px) with semantic space role names for common layout patterns (--space-component-padding, --space-section-gap) preventing the one-off gap: 14px that breaks the rhythm. Shadow scale with named elevation levels (resting, raised, floating, overlay) correlated to the component's position in the visual stack. Border radius scale with semantic aliases matching component types (card, button, input, pill, circle) rather than a loose set of pixel values that different developers apply inconsistently.