TL;DR
The Interop project is preparing its 2027 focus areas, and Mozilla has created a ranking system for developers to vote on requested web features. A developer’s preview highlights CSS proposals such as functions, custom corner shapes and border shapes, but the final Interop 2027 selections and broader browser availability are not confirmed.
Mozilla has created a ranking system for developers to vote on requested web-platform features as browser vendors plan Interop 2027, a project intended to improve support across browsers. The feature list has not been finalized; a developer’s preview points to several CSS proposals that could receive attention, but their inclusion and eventual cross-browser availability remain uncertain.
The Interop project brings together Google, Apple, Microsoft and Mozilla, as well as web-platform contributors Igalia and Bocoup. According to the source report, participating teams use selected focus areas to coordinate work on compatibility across browsers. The ranking data is expected to help inform next year’s choices, not to guarantee that any particular feature will be selected.
The report’s author highlights CSS functions, corner-shape and border-shape among the proposals he voted for. CSS functions would let authors define reusable calculations or values in CSS. Corner-shape would offer alternatives to the usual rounded corners, while border-shape would allow custom borders built from lines and curves. These are examples from the author’s list, not a confirmed Interop 2027 agenda.
The report lists the features it discusses as supported in Chrome 155 and Edge 154, but not Firefox 157 or Safari 27 at the time described. That support information reflects the report’s October 2026 snapshot. A feature’s presence in one browser, or a developer’s vote for it, does not establish that all major browsers have implemented it.
How Interop Priorities Affect CSS
For developers, coordinated compatibility work can reduce the gap between a feature being available in one browser and being dependable across the browsers used by an audience. That can influence whether teams adopt a new CSS capability directly, use it only as an enhancement, or continue relying on older techniques.
The source report points to CSS Subgrid as an example of the project’s potential effect: it says the feature was added to Interop 2023 after years of uneven progress and became widely available across modern browsers by that year’s end. That example is the author’s account of an earlier effort; it does not establish how quickly any candidate in the 2027 process will gain support.
For people building sites and applications, the immediate practical takeaway is to distinguish experimental or unevenly supported features from stable cross-browser tools. Even when a proposal can improve visual design or simplify code, compatibility still determines whether it can be used for core functionality or should be treated as an optional enhancement.
As an affiliate, we earn on qualifying purchases.
From Subgrid to 2027 Planning
Interop is a recurring collaboration among browser vendors and other web-platform organizations. Its stated aim is to improve compatibility by coordinating work around selected technologies. The source report says that features chosen as focus areas often reach close to full support across major browsers within a year, though it does not provide a general measurement or guarantee for future selections.
Subgrid is the report’s example of a prior result. Firefox implemented it in 2019, while adoption elsewhere moved more slowly. After it became an Interop 2023 focus, the report says support spread across modern browsers by the end of that year. The example helps explain why developers may seek coordinated attention for newer CSS features.
As of the report’s October 2026 publication, Interop 2027 was still being planned. Mozilla’s ranking system is intended to collect preferences that can inform the selection process. The author uses his own top 10 votes to discuss possible directions for CSS; those selections should not be confused with an official shortlist.
As an affiliate, we earn on qualifying purchases.
Which CSS Features Make the Cut
The final Interop 2027 focus areas are not identified in the source material. It is unclear how the ranking results will be weighed, when the selected list will be announced, or whether the CSS proposals discussed by the author will be included.
Browser support could also change after the report’s stated October 2026 snapshot. The material gives support figures for particular browser versions, but does not establish a release schedule for Firefox or Safari, or a timeline for any feature to become interoperable. The author’s expectation that a feature could spread more quickly if prioritized is a prediction, not a confirmed outcome.
CSS frameworks for modern web development
As an affiliate, we earn on qualifying purchases.
As an affiliate, we earn on qualifying purchases.
The Selection and Support Timeline
The next step is for the Interop 2027 planning process to use the ranking information and determine which focus areas to pursue. The source does not give a decision date or confirm when the chosen areas will be published. Until the selections are announced, developers should treat the author’s feature list as a preview of possibilities rather than a roadmap.
After priorities are set, progress will depend on browser implementation and testing. Developers can track support in the browsers and versions relevant to their audiences, and test newer CSS carefully before relying on it for essential behavior. Wider availability will need to be confirmed through actual cross-browser support, not inferred from a vote or a proposal’s inclusion.
browser compatibility testing tools
As an affiliate, we earn on qualifying purchases.
As an affiliate, we earn on qualifying purchases.
Key Questions
What is Interop 2027?
Interop 2027 is the upcoming cycle of the Interop collaboration, in which browser vendors and other contributors coordinate work intended to improve support for web technologies across browsers. Its focus areas were still being planned in the source report.
Have the CSS features in the report been selected?
No. The report describes features its author voted for, including CSS functions, corner-shape and border-shape. It does not say those proposals have been officially selected for Interop 2027.
What does the Mozilla ranking system do?
According to the report, it lets people rank or upvote requested features. The results are intended to help inform Interop 2027 planning; the report does not say that votes alone determine the final agenda.
Are the proposed CSS features available in every browser?
No. The report’s October 2026 support snapshot lists the discussed features as available in Chrome 155 and Edge 154, but not Firefox 157 or Safari 27. Support may change, so developers should check current browser data before using a feature.
Source: hn
