Verified scope and progressive enhancement
Browser support
The fully enhanced target starts at Chrome/Edge 114, Firefox 125, and Safari 17. Automated tests exercise pinned Chromium, Firefox, and WebKit builds; minimum product versions remain feature-derived targets.
Test matrix
| Engine | Environment | Coverage | Status |
|---|---|---|---|
| Chromium 151 | Windows and Ubuntu, Playwright 1.62.1 | Functional, responsive, keyboard, axe, and OS-specific visual baselines | Automated |
| Firefox 153 | Windows and Ubuntu, Playwright 1.62.1 | Functional, responsive, keyboard, axe, themes, RTL, dialog, details, and native controls | Automated |
| WebKit 26.5 | Windows and Ubuntu, Playwright 1.62.1 | Same non-visual browser contracts, with explicit progressive popover handling | Automated engine |
| Safari 17+ | Product target | Feature-derived minimum; WebKit automation is supporting evidence | Safari application not run directly |
Features that set the baseline
color-mix()- Builds token-derived surfaces; unsupported declarations are ignored, so base colors and borders remain.
:has()- Adds parent-aware invalid and disabled styling; native control semantics still work without it.
- Popover API
- Native non-modal overlay enhancement. Use
detailsor consumer behavior when older browsers matter. dialog- Provides modal semantics and focus handling for drawers and dialogs.
overflow: clip- Prevents page-level horizontal overflow; local scroll containers remain available.
Fallback policy
Older engines should retain semantic document order, readable text, native form controls, and local table/code overflow. They may lose mixed surface colors, relational state styling, native popover behavior, balanced headings, or selected animation. FrameBaseCSS does not include polyfills and does not claim legacy browser support.