Base UI Handbook: Foundations

Use this skill when a question is cross-component and not about one concrete component’s API.

Scope

• Styling model (className, style, render, state callbacks)
• CSS hooks (data-* state attrs, CSS vars, data attributes from popup placement)
• Animation and transition attributes
• Composition patterns with nested render callbacks
• Customization and behavior tuning (open, onOpenChange, reason-based handlers)

Routing cues

• "style hooks", "Tailwind", "CSS module", "composition", "render prop", "animation", "transition", "customization", "custom behavior", "event reason" → this skill

Canonical references

• https://base-ui.com/react/handbook/styling
• https://base-ui.com/react/handbook/animation
• https://base-ui.com/react/handbook/composition
• https://base-ui.com/react/handbook/customization
• https://base-ui.com/react/overview/accessibility

Maintenance

• Snapshot date: 2026-02-13
• Refresh cadence: quarterly
• Upstream changelog anchor: https://github.com/mui/base-ui/blob/master/CHANGELOG.md

References

• Foundation source map
• Composition patterns and caveats