Cascading Style Sheets, or CSS, is a language used to specify the visual appearance of a Web page—in contrast to HTML (HyperText Markup Language), which is a markup language that defines the structure of a document for distribution on the Web. HTML tells a Web browser how the content is organized on the page, whereas CSS tells the browser how it should look. CSS3, an abbreviation for CSS Level 3, is the next generation of this style language that adds several new capabilities.