CSS (Cascading Style Sheets) is a language that defines the appearance of a document written in a markup language (e.g., HTML ).
Thus, the elements of the web page created with HTML given the desired appearance using CSS: colors, spaces between elements, fonts, thus separating the structure of the presentation.
This separation between the structure and the presentation is significant since it is only by changing the CSS that the appearance of a web page is completely modified. It makes it possible, among other things, for users to use custom style sheets (such as high contrast or accessibility style sheets ).
The W3C defines the specifications of the CSS standard. Later, browsers try to implement those specifications, so that web pages look the same on all of them.
Browsers are increasingly complying with the CSS standard. For example, Internet Explorer 6 met the standard by only 12%, while Internet Explorer 9 met 95%. That is why web pages should be make out following the CSS standard and not the specifications of a specific browser.
We must also try to keep the browser updated since, as they meet the standard, they add features that they did not have before.