The first thing to understand when approaching the topic of CSS is when to use a styling language like CSS and when to use a markup language such as HTML.

• All critical website content should be added to the website using a markup language such as HTML.
• Presentation of the website content should be defined by a styling language such as CSS.

Blog posts, page headings, video, audio, and pictures that are not part of the web page presentation should all be added to the web page with HTML. Background images and colors, borders, font size, typography, and the position of items on a web page should all be defined by CSS.

It’s important to make this distinction because failing to use the right language can make it difficult to make changes to the website in the future and create accessibility and usability issues for website visitors using a text-only browser or screen reader.