For a web page or internet content to be attractive and appealing, an important aspect is the presentation semantics. This basically deals with the look and formatting of the web content. CSS is the short form of Cascading which is a style sheet language used to write the presentation semantics when a document is written in a markup language. Basically CSS uses simple syntax and a number of regular English words to specify the names of various style properties. The concept of style sheets has been in existence since the 1980s. CSS basically provides style information to web documents. Cascading Style sheets or CSS has evolved along with HTML over the past two decades or so. CSS can define the text alignment, size, font, color spacing, borders and layout as well as many other typographic features of a web page or web content on the internet.
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There has been a lot of innovation and upgrades over the years for CSS. Each new version of the CSS tends to build on the previous version that means it upgrades and adds more features to the existing version. A widely used version is the CSS3. CSS2 was a large specification defining various features and CSS3 is a little different as compared to that. CSS3 is divided into separate documents called modules. Each module works on different capabilities and extends features. Each module is developed separately and the status and upgrades of each module differ from the other. So CSS3 is sort of a grouping of all these new modules of CSS.
Many of the features developed in CSS3 are experimental and the statuses and level of completion vary. Also many are not yet widely used and also are not supported by browsers especially not supported by older browsers. So CSS3 is a general term that refers to a wide range of evolving CSS features and CSS3 is not a general specification. CSS3 is a popular style sheet language and many of the features that are developed under CSS3 are implemented by web designers and programmers to create a better formatting and presentation of their websites and online documents.