CSS stands for Cascading Style Sheets

To style a web page with CSS, you will need a document that has been marked up in HTML. Given the document, you write rules to style the elements in your HTML. This can be a p element or an img element, anything that you want to style yourself.

CSS styling rules can either be included at the top of your document in the head section of your HTML but typically it is preferable to keep your CSS in a separate file of its own known as the styling sheet.

The browser renders a page's elements using the CSS rules that describe them.