Dynamic stylesheets allow the styles to change dynamically (not surprisingly), like
<H1 onmouseover="this.style.color = 'red';">stuff</H1>
Pretty cool merging of CSS and dynamic scripting, I think. You didn't finish your questions, if this might help answer it. You can keep the styles in a separate document, or you can include the styles within your document. If they are in a separate document, you just need to link to that document as shown by linkjj above.