CSS custom functions are promising, but Interop proposals are not a shipping promise
Josh Comeau previews features he wants prioritized in Interop 2027, the cross-browser compatibility effort. CSS custom functions could package reusable calculations and return CSS values, while corner-shape provides alternatives to ordinary rounded corners. His examples explain the mechanics, but the article is a wishlist rather than an agreed release schedule. Browser support differs, so a proposed focus area should not be mistaken for universally deployable CSS.
Josh W. Comeau · Oct 20, 2026
Why it matters
Useful frontend experiments need a clear separation between an appealing feature, an interoperability proposal and support in the browsers a product serves.
More context
The inspected opening sections demonstrate @function and corner-shape. The linked official @function proposal remains open and labeled a focus-area proposal, with limited availability recorded. Try isolated examples and check target browsers before using them in a required layout or component behavior.
Keep in mind
Interop participation and developer votes do not guarantee a particular implementation date. The article’s browser snapshots are time-specific, and experimental support does not establish production coverage across engines.
Original read