Cascading Style Sheets (CSS) is a style sheet language used for describing the presentation of a document written in HTML or XML. Coursera's CSS catalogue teaches you how to visually manipulate web design. You'll learn everything from the basic principles of CSS, layout and positioning, to responsive design techniques, animations, and preprocessors. By mastering CSS selectors, specificity, box model, flexbox, and grid, you'll be able to create beautiful, efficient, and dynamic websites and web applications, enhancing your skills as a web developer, designer, or digital marketing specialist.