CSS (Cascading Style Sheets) is a computer language used to describe the look and formatting of a document written in HTML. CSS allows you to style the elements of your webpage, such as changing the colors, fonts, sizes, and layout. To apply CSS to an HTML document, you can use both external and internal methods. External CSS: You can create a separate CSS file with a .css extension, which contains all the CSS code for your webpage. Then, link this external CSS file to your HTML document using the link tag in the head section, like this how i did it above. Internal or In line is in the HTML file. It uses the same properties as external but has better priorty than external. In line is in the tag whileinternal uses the style tag. Then you can indicate what tag you want to change like p or hr or h1. Then you indicate what you want to style like font family or color.