What is HTML and CSS?

HTML for content, CSS for presentation

HTML (HyperText Markup Language) is a language used by computers to display the content of a web page. CSS (Cascading Style Sheets) are used to create the presentation and style of an HTML document.

The advantage of keeping the content (HTML) and presentation (CSS) separate is that you can update an entire website by modifying a single line of CSS code which removes the need to edit every single page on a website to make a simple change.