Once a style is specified, there are three ways to attach it to an HTML
document:
Inline Styles:
This attaches a style definition to a specific HTML tag within the
document using the new "style=" attribute in all HTML tags. This option
should be avoided whenever possible.
Document Styles:
This uses the <style> tag in the <head> section of the
document to insert a style sheet which defines styles for the entire
document. This lets us, for example, say every <h1> tag in this
document will display text in navy letters.
External Style Sheets:
This puts the style sheet in a separate file which we link to using
the <link> tag in the <head> section of the document. This
lets many different html documents share one style sheet.