Microsoft and Google are partnering to promote web browser compatibility around a number of CSS (Cascading Style Sheets) features, with an effort called #Compat2021.

Also involving open source software consulting firm Igalia and the broader web community, #Compat2021 aims to improve compatibility in five specific areas:

• CSS Flexbox, a CSS module that defines a CSS box model optimized for user interface design and the layout of items in a single direction.
• CSS Grid, for dividing a page into regions or defining the relationship in terms of layer, position, and size, between parts of a control built from HTML primitives.
• CSS Position: sticky, or sticky positioning, which is akin to a hybrid of relative and fixed positioning.
• CSS aspect-ratio property, pertaining to a CSS property setting a preferred aspect ratio for the box, to be used in the calculation of auto sizes and other layout functions.
• CSS transforms, for rotating, scaling, skewing, or translating an element.

The joint working group involved in the project identified these focus areas based on the number of related bugs in each vendor’s tracking system, feature usage data, survey feedback, CanIUse data, and web-platform-tests test results.

While working group members will focus on their respective implementations, the Microsoft Edge team plans to contribute fixes to the Google-sponsored Chromium project to pass all CSS Grid tests in 2021 and to support improving interop across browsers.

#Compat21 was announced on March 22. Progress on the project can be tracked on the Compat 2021 dashboard.