CSS Gets Functions, Custom Shapes, and More in Interop 2027

Browser vendors have coordinated through the Interop project to standardize web technology support across Chrome, Firefox, Safari, and Edge. Features added to Interop typically reach near-universal adoption within a year, as demonstrated by CSS Subgrid’s rapid cross-browser rollout after 2023’s inclusion. The community is now voting on priorities for Interop 2027.

Key proposed features include CSS functions—parameterized declarations similar to JavaScript functions that can encapsulate reusable property values and mathematical operations like trigonometric calculations. The corner-shape and border-shape properties would expand beyond traditional rounded corners, enabling bevels, squircles, and arbitrary shapes drawn with curves and lines. Unlike existing workarounds, these actually reshape the element’s border box, ensuring shadows and outlines follow the new geometry correctly.

Additional proposals extend the Anchor Positioning API with container queries to detect fallback positioning states for tooltips, and an inherit() function that transforms inherited values through calculations rather than copying them directly. Some features are already available in Chromium but await broader adoption, making them viable as progressive enhancements today.