Stylesheets separate style from content
The content, along with tags indicating different kinds of meaning (headings, lists, emphasis), is placed in the HTML file. A separate stylesheet file controls the appearance of that content.
You can specify styles for a particular HTML tag
For example, you could specify the fonts for all headings.
You can be more specific
It is also possible to be more specific by using the class attribute in HTML, which allows you to control the appearance of some occurrences of an element independently of others.
The <div> tag lets you divide a page into larger areas, each of which can have its particular style.