Cascading Style Sheets or CSS is the language used to describe the presentation of HTML or XML documents, this includes several XML-based languages such as XHTML or SVG. CSS describes how the structured element should be rendered on the screen, on paper, spoken or in other media. CSS is a specification developed by the W3C (World Wide Web Consortium) to allow the separation of the contents of documents written in HTML, XML, XHTML, SVG, or XUL from the presentation of the document with style sheets, including such elements such as colors, backgrounds, margins, borders, fonts ..., modifying the appearance of a web page in a simpler way, allowing developers to control the style and format of their documents. The CSS language is based on a series of rules that govern the style of elements in structured documents, and that form the syntax of style sheets. Each rule consists of a selector and a declaration, the latter is bracketed and consists of a property or attribute, and a value separated by two points. There are several versions: CSS1 and CSS2, CSS3 is still under development by the CSS WG (Cascading Style Sheets Working Group). The current browsers implement CSS1 quite well since 1999 (three years after its launch) although depending on the brand and browser version there are some small differences in implementation. The first browser to fully support CSS1 has been Internet Explorer 5.0 for the Macintosh in 2000, previously the one that best supported CSS1 had been Opera, then other browsers have also been implementing it. However, CSS2 (launched in 1998) is only partially implemented in the most recent browsers, varying in these levels of implementation.
