External CSS - Link External Stylesheet to HTML Page : Web Programming with Python and JavaScript
With an external style sheet, you can change the look of an entire website by changing just one file!
Each HTML page must include a reference to the external style sheet file inside the link element, inside the head section.
An external style sheet can be written in any text editor, and must be saved with a .css extension.
The external .css file should not contain any HTML tags.