World Wide Web Consortium's CSS Page that includes links to standards and other reference pages. Also includes news on CSS happenings. Examples in Each Chapter. This CSS tutorial contains hundreds of CSS examples. With our online editor, you can edit the CSS, and click on a button to view the result. A free service from W3C that checks HTML and XHTML code against the W3C Web Accessibility Guidelines. Unicorn - W3C's Unified Validator. Improve the quality of the Web. By URI; By File Upload; By Direct Input; Select a task Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in a markup language. Although most often used to. function myFunction() var x = document.getElementById( demo ); x.style.fontSize = 25px ; x.style.color = red ; W3C CSS Validation service enables you to check your CSS code for validity, and warns you if you are using browser specific code. The World Wide Web Consortium (W3C) is an international community where Member organizations, a full-time staff, and the public work together to develop Web standards.