A style sheet may be imported with CSS's @import statement. This statement may be used in a CSS file or inside the style element:
<style type="text/css" media="screen, projection">
<!--
@import url(http://www.example.com/style.css);
@import url(/stylesheets/rainbow-themed.css);
dt { background: yellow; color: black }
-->
</style>
If you're just wanting to include CSS in your HTML page, use a link:
<link rel="stylesheet" href="css/style.css" />
