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.
If you have been working just a bit with web design, you probably know that there can be a big differences in how a webpage is presented across different browsers. It can be very frustrating and time-consuming to create a webpage which can be viewed in Mozilla, Internet Explorer, Opera and all the rest of the existing browsers.
The idea of having standards is to agree upon a common denominator on how to use web technologies. This means that by observing the standards, a webdeveloper has a certainty that what he or she does will work in a more appropriate manner across different platforms. We therefore recommend that you back up the work carried out by the W3C and validate your CSS in order to observe the standard.
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.
If the validator does not find any errors; this picture will be shown, which you can put on your website to illustrate that you are using validated coding:
The validator can also be found at this link: http://jigsaw.w3.org/css-validator/