We learned to structure the content of an HTML document.In terms of design and style, these pages still leave a lot to be desired. A CSS file essentially describes how specific elements of HTML should be displayed in the browser. CSS stands for Cascase style sheets and layouts and styles the HTLM elements and structure of a page. So, CSS is a styling language, and you can write css code between the head-tag, of you can create a seperate css file (a file with .css extension).
What is CSS?
Working with CSS