CSS or Cascading Style Sheets is a style sheet language used to describe the appearance of web pages written in HTML and XML. CSS provides a way to separate the appearance of a web page from its content, making it easier to maintain and update the design of your website.CSS works by defining rules that describe how HTML elements should appear on a web page. These rules can be defined in an external style sheet that can be linked to one or more HTML pages, or they can be defined directly within the HTML document using the “style” attribute.CSS contains a variety of features for controlling layout, typography, colors, and other aspects of web page design. For example, CSS allows developers to specify the size, position, and spacing of elements on a web page, as well as the font size, weight, and style of text.

CSS includes media queries that a developer can use to create responsive designs that adapt to different screen sizes and devices, and animations that a developer can use to add dynamic effects to his web pages. Advanced features such as transitions are also included.CSS is used by almost every website on the Internet, making it an essential skill for web developers and designers. There are many resources for learning CSS, including online tutorials, books, and courses. Popular CSS frameworks such as Bootstrap and Foundation also help optimize the development of  responsive and mobile friendly his website.