What is the function of CSS in web design?

What is the function of CSS in web design?

CSS is used for making attractive and stylish the HTML page. Using CSS we can change and make the layout, font, color of the any xml based language.
CSS is also used to make responsive web-site.

CSS is a Most Important Part Of WEB Designing. If You Became a Web Designer so You Can learn all the Codes of CSS & CSS3.