App Interface Guideline: Theming — Light/Dark Contrast. Keywords: dark mode contrast tokens. Platform: iOS/Android/React Native. Description: Ensure sufficient contrast in both light and dark themes. Do: Use semantic tokens and test both themes. Don't: Reuse light-theme grays directly in dark mode. Good Example: colors.textPrimaryDark = '#F9FAFB'. Bad Example: colors.textPrimaryDark = '#9CA3AF' on '#111827'. Severity: High.