“CSS” is an acronym for Cascading Style Sheets, a web-based markup language used to describe the look and formatting of a website to the browser, most commonly used in HTML or XHTML web pages but also applicable to XML documents, including plain XML, SVG and XUL. “CSS3” simply refers to the latest incarnation of CSS, with additional capabilities far beyond the scope of the first two generations.
Because of its modular structure, CSS3 allows developers to build content-rich web pages with relatively lightweight code requirements. That means fancier visual effects, better user interfaces and most importantly, cleaner pages that load faster than ever before. Simply put, CSS3 is the presentation layer of a web page that leads the charge for all of the other technologies buried within.
CSS3 finally brings the promise of desktop-style layout to web pages, complete with graphic elements such as drop shadows, gradients, border effects, multi-column layouts and much more.