What more is there to know about HTML?
HTML can be coded in many different ways. And browsers can read HTML in just as many ways. You could say that HTML has many dialects. That is why some websites look different in different browsers.
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 web developer 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 HTML and CSS in order to observe the standard.
To make it easier to observe the CSS standard, W3C has made a so-called css validator which reads your stylesheet and returns a status listing errors and warnings, if your CSS does not validate. Validate your code with the CSS Validator.
HTML validator can be found here.