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