To make it easier to observe the CSS standard, W3C has made a so-called validator which reads your stylesheet and returns a status listing errors and warnings, if your CSS does not validate. To make it easier for you to validate your stylesheet, you can do it directly from this webpage. Simply replace the URL with the URL of your stylesheet below and click to validate. You will then be informed by the W3C site if there are any errors found.

W3C is the World Wide Web Consortium, which is an independent organization that manages code standards on the web (e.g. HTML, CSS, XML and others). Microsoft, The Mozilla Foundation and many others are a part of W3C and agree upon the future developments of the standards.