CSS ( Cascading Style Sheets ) is a style sheet language used to apply a specific ‘look and feel’ to a Web page written in a markup language such as HTML.
CSS saves time as it can control styling of multiple Web pages at once. CSS transforms the style to a Web page by interacting with HTML elements. If you can imagine that HTML is the skeleton then CSS are the clothes.
Marc has used CSS all his career, and has knowledge in CSS | CSS2 and CSS3.