Cascading Style Sheets Standard Boasts Unprecedented Interoperability

Author(s) and publish date


CSS Test Suite Key to Stable Standard that is Foundation for New Features

Testimonials — 7 June 2011 — W3C, the standards body for the suite of technologies that together provide an Open Web Platform for application development, today announced new levels of support for Cascading Style Sheets (CSS), the language for adding style to Web content. W3C released an update to the core CSS standard (2.1) to reflect the current state of support for CSS features, and to serve as the stable foundation for future extensions.

CSS has been in widespread use as an Open Web technology for more than a decade, but it took many years for implementations and the specification to converge. The collective efforts of the CSS Working Group, implementers, contributors to the CSS Test Suite, and the W3C CSS community have made interoperable CSS a reality for the Open Web. More than 9000 CSS tests have made it easier for designers to create style sheets that work across browsers, and across devices.

"This publication provides me with an opportunity to congratulate and thank the CSS Working Group, and all of the developers that have made CSS a success," said Bert Bos, co-inventor of CSS and Editor of CSS 2.1. "This publication crowns a long effort to achieve very broad interoperability. Now we can turn our attention to the cool features we've been itching to bring to the Web."

CSS interoperability plays an important role in the rapid adoption of W3C's Open Web Platform, which also includes HTML5, SVG, WOFF, APIs for geolocation and offline storage, real-time communications, and a host of other technologies for building rich, interactive applications.

A Stable Platform for Innovation

This year we celebrate the 15th anniversary of CSS, the powerful toolkit that makes it easy to create visually engaging pages and applications, to deploy experimental features safely, to maintain style independently of content, and to adapt pages to new devices.

"People have asked us 'Why is CSS 2.1 taking so long?'", said Daniel Glazman, CSS Working Group Co-chair. "CSS 2.1 is a really large collection of formatting features, and we had to not only carefully review and specify all the potential interactions between them, but also learn from existing implementations and of course tests. Time ensured quality and interoperability."

The current interoperability makes it easier than ever for developers and designers to enrich the toolkit. W3C expects future additions to CSS to be organized as independent modules, allowing smaller, more focused feature sets to progress and stabilize at their own pace. Some of these new features are already supported in browsers and other software in draft form (using the built-in CSS prefix mechanism designed for experimentation). As interoperability improves for each one, developers can transition to the standard to simplify their code. The CSS Working Group also publishes snapshots of which CSS features are supported interoperably in browsers; see, for instance, the most recent CSS Snapshot.

"Now that we have published CSS 2.1 as a Recommendation," said Peter Linss, co-chair of the CSS Working Group, "the Working Group can focus its efforts on rapidly advancing CSS with new modules for improved layout controls, new visual effects, broader international support, and more."

New Standards for Colors, Profile for MathML also Published

W3C published two other standards as well that are widely deployed and now build on the stable CSS 2.1 base: CSS Color Module Level 3, and A MathML For CSS Profile.

The Colors module provides new, more convenient ways to specify colors and transparency for text, borders, and backgrounds.

The second illustrates how various pieces of the Open Web Platform work together. "MathML For CSS Profile," in conjunction with MathML, will make it easier for authors to put math expressions on the Web and have them rendered faithfully.

About the World Wide Web Consortium

The World Wide Web Consortium (W3C) is an international consortium where Member organizations, a full-time staff, and the public work together to develop Web standards. W3C primarily pursues its mission through the creation of Web standards and guidelines designed to ensure long-term growth for the Web. Over 325 organizations are Members of the Consortium. W3C is jointly run by the MIT Computer Science and Artificial Intelligence Laboratory (MIT CSAIL) in the USA, the European Research Consortium for Informatics and Mathematics (ERCIM) headquartered in France and Keio University in Japan, and has additional Offices worldwide. For more information see

Media Contact

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Testimonials for Cascading Style Sheets Standard Boasts Unprecedented Interoperability

Adobe · Antenna House · Disruptive Innovations · HP · Microsoft · Mozilla · Nokia · Opera Software · University of Oviedo


Adobe congratulates the W3C and the CSS Working Group on the release of CSS 2.1, a significant move forward with improved inter-operability, which will make it easier for tools to use the sophisticated features that have been incorporated in this release. The inclusion of media based styling so that the presentation can change based on the display context (desktop, mobile, print, audio) is important both for tool makers as well as to make the web more accessible. The clearer definitions and improvements to the specification based on the feedback of the community will lead to a more predictable and consistent web. Finally, CSS 2.1 will also improve the typographic quality of content on the web.

Adobe believes that the release of this specification strengthens the W3C position as the leader in the creation of an open web platform, and reflects the ability of the W3C to act as an organization which can gain broad cross-industry consensus. Adobe also congratulates and thanks all of the companies and organizations which participated over time in the CSS WG to move the web forward.

Arno Gourdol, Director of Engineering, Runtime Foundation, Adobe Systems

Antenna House

Antenna House is very pleased to see the advancement of CSS level 2 revision 1 to Recommendation. We are proud of our contribution to this effort, both as a member of the CSS working group and as the provider of AH Formatter which enables web designers to use CSS to add print and PDF output to their systems through the features and functionality that Antenna House has developed in support of the Recommendation.

I personally look forward to Antenna House continuing its work both with the W3C and in the development of CSS support within Formatter.

Tokushige Kobayashi, President, Antenna House, Inc.

Disruptive Innovations

Back in 1998, when CSS 2 became a W3C Recommendation, it provided the Web authors' community with a new exciting set of features in terms of stylesheets and formatting properties. But because humans are only humans, CSS 2 went too far too fast and implementations never completely matched the specification and users' expectations. Some parts of the Recommendation were under-specified, some raised complex technical issues, and some were even unimplementable given the state of the art at that time.

After many years of extremely hard work, the CSS Working Group has now revised the specification and released CSS 2.1, a major rewrite of the document. Based on a Test Suite containing tens of thousands of tests and checking interoperable implementability across browsers of all features in the document, CSS 2.1 establishes a new common ground for the Web that all browser vendors agree on. Backed by consensus and strong implementation commitment from the industry, the release of CSS 2.1 lays the foundation for the future CSS 3, and even more interoperable stylistic power offered to Web authors.

As an HTML/XHTML Wysiwyg editor vendor implementing CSS, Disruptive Innovations would like to congratulate the W3C for this major step forward. As the employer of one of the co-chairmen of the CSS Working Group, we would like to congratulate and thank all present and past Members of the Group and all present and past Invited Experts to the Group for their hard work. This W3C success is their success.

Daniel Glazman, CEO, Disruptive Innovations SAS


HP is extremely pleased to see the Cascading Style Sheets Level 2 Revision 1 specification become a W3C Recommendation. It is grateful to all those companies and individuals whose hard work contributed to this significant milestone, including the CSS Working Group’s Co-Chairs, Daniel Glazman of Disruptive Innovations and Peter Linss of HP.

In addition to being one of the more complicated specifications created by the W3C, it is also one of the most thoroughly tested. The unprecedented level of CSS conformance by all major browsers marks the beginning of a new era for the web.

The completion of CSS 2.1 serves as a solid foundation upon which the CSS Working Group can build. We at HP are excited to anticipate what's in store for the future of the web and are proud to be a part of W3C’s role in shaping that future.

Jim Bell, Director of Industry Standards Program Office, Hewlett-Packard Company


CSS is a foundational capability for the web and this is a significant milestone for W3C. CSS 2.1 demonstrates that the combination of a stable specification coupled with a test suite is the only way to achieve real interoperability. This is a huge step towards a more interoperable web.

Jean Paoli, General Manager, Interoperability Strategy at Microsoft.


The CSS 2.1 specification and its test suite are a huge step forward in making browsers display Web pages the same way, and provide a strong foundation for future development of CSS. We are continually improving our implementation of CSS in Mozilla Firefox based on this work. As we and other browsers do this, it gives Web authors a larger set of features they can use reliably for styling on the Web.

L. David Baron, Mozilla


Nokia is pleased the CSS 2.1 specification has reached the "Recommendation" stage of the W3C's process and the CSS Working Group has produced a comprehensive test suite for this specification. The CCS 2.1 specification is the most widely used CSS standard and has greatly improved the mobile Web experience. CSS 2.1 enables consistency in implementation across devices and reflects proven best practices based on over ten years of use since CSS 2.0 reached the Recommendation stage in 1998. The end result is a richer, more compelling experience for mobile phone users world wide across a very broad range of devices. Nokia supports commonly used Web standards, and has shipped millions of devices supporting CSS 2.1. With the strong foundation of CSS 2.1, we believe Web developers can build solid mobile Web experiences for the next billion mobile consumers.

Jari Alvinen, Director, Compatibility and Industry Collaboration, Nokia

Opera Software

Opera is very pleased to see CSS 2.1 become a W3C recommendation. As part of our goal to support developers by ensuring that Web Standards work interoperability, as well as continually enhancing the capability of the Web as a platform, this is an important milestone. We look forward to W3C focusing now on standardising new features and further improving the specification of styling for the Web with CSS3.

Charles McCathieNevile Opera Software, Standards Group

University of Oviedo

After several years of hard work CSS 2.1 is ready to be released as a W3C recommendation. We firmly believe that this long journey has been worthwhile. From the University of Oviedo we encourage W3C to continue with the evolution of CSS and congratulate current and past members of the CSS Working Group for making the Web a better place.

Xabiel García Pañeda, Director of R&D Management Area, University of Oviedo

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