For several years, major browser vendors—Google, Apple, Microsoft, and Mozilla, along with Igalia and Bocoup—have collaborated on Interop, a project designed to improve cross-browser support for web technologies. According to the source, the initiative has proven remarkably successful, with focus areas often reaching near-100% browser support within a year of adoption.
CSS Subgrid exemplifies this success. The feature, a powerful extension to CSS Grid enabling new layout possibilities, was implemented in Firefox in 2019 but saw limited adoption elsewhere. After being added to Interop 2023, it achieved widespread availability across all modern browsers by year’s end.
As 2026 concludes, planning for Interop 2027 is underway. Mozilla has created a ranking system allowing developers to vote on the most-requested features, with results informing the selection of next year’s priorities.
Among the top proposed features is CSS functions, which would allow developers to define reusable CSS operations similar to JavaScript functions. According to the source, this capability is already implemented in Chromium browsers and could enable uses like converting between polar and cartesian coordinates for animations.
Another priority is the corner-shape property, which would provide alternatives to border-radius for connecting the edges of DOM nodes. Options include bevels and squircles—the latter using superellipses to produce smoother curves, an approach Apple has employed for years. The source notes that corner-shape would modify the actual border-box, allowing borders, outlines, and shadows to correctly follow the altered shapes.
Border-shape is a companion proposal offering lower-level control, enabling developers to draw custom borders using straight lines, arcs, and Bézier curves.
Anchor Positioning, prioritized in Interop 2026 and now widely available, allows elements to anchor to others—useful for tooltips and floating UI elements. A Level 2 version adds container queries to detect whether elements are using fallback positions.
Another proposed feature is the inherit() function, which would allow CSS properties to reference and transform inherited values using calc(), though the source notes this remains preliminary.
Key facts
- Browser vendors collaborating on Interop have achieved near-100% support for adopted focus areas within a year
- CSS Subgrid went from Firefox-only (2019) to widespread availability after joining Interop 2023
- CSS functions are already implemented in Chromium and could enable coordinate transformations for animations
- Corner-shape property would offer alternatives like bevels and squircles to traditional border-radius
- Interop 2027 priorities are being determined by developer voting on a Mozilla-created ranking system