How To Add CSS How To Add CSS Three Ways to Insert CSS There are three ways of inserting a style sheet: External CSS Internal CSS Inline CSS External CSS: 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. Internal CSS: An internal style sheet may be used if one single HTML page has a unique style. The internal style is defined inside the <style> element, inside the head section. Inline CSS: An inline style may be used to apply a unique style for a single element. To use inline styles, add the style attribute to the relevant element. The style attribute can contain any CSS property.