External Style Sheet
If you have to give same look and feel to many pages then it is a good idea to keep all the style sheet rules in a single style sheet file and include this file in all the HTML pages. You can include a style sheet file into HTML document using <link> element. Below is an example.
<head>
<link rel=”stylesheet” type=”text/css” href=”yourstyle.css”>
</head>
Internal Style Sheet
If you want to apply style sheet rules to a single document only then you can include those rules into that document only. Below is an example :
<head>
<style type=”text/css”>
body { background-color: pink; }
p{color:blue;20px;font-size:24px}
</style>
</head>
Inline Style Sheet
You can apply style sheet rules directly to any HTML elemet. This should be done only when you are interested to make a particular change in any HTML element only. To use inline styles you use the style attribute in the relevant tag. Below is an example:
<p style=”color:red;font-size:24px;”>Using Style Sheet Rules</p>