- Create styles/tokens.css with CSS custom properties and dark theme
- Create styles/global.css with resets, shell layout, and navigation
- Create styles/utilities.css with generic utilities and primitives
- Create styles/syntax-highlight.css with Prism.js theme
- Update main.tsx to import the 4 new style files
- Keep styles.css intact for backward compatibility
Quality gates: build (pass), lint (pass)
Refs: repo-restructure Task 2.1