- Hyper-Text Markup Language (HTML) provides the structure and content
- Cascading Style Sheets (CSS) determine how that content should appear visually
We often refer to this division of responsibility as the separation of concerns. By placing all responsibility for appearance on a CSS file, we can refresh the look of a web application simply by replacing the old CSS file with a new one. Similarly, we can create a new page in our site that looks and feels like the rest of the site by creating a new HTML page that links to the site’s existing CSS files.