Cascade Style Sheet (CSS) is the scripted style sheet language used to control the appearance of hypertext markup written in HTML5. In simple words, you will use CSS to describe the layout and style of a web page. As HTML5 is the barebones structure of any webpage, the CSS enables you to make it more presentable and pleasant looking.
CSS3 simplifies the process of designing your websites such as controlling the colors, choosing background images, selecting fonts, paddings, margins, adding space between paragraphs, and a myriad of other effects.
The CSS3 is the latest standard of Cascade Style Sheet and the coming lectures will cover some of its most important modules.