Improve Your Site's SEO Score with CSS
Cascading style sheets (CSS) can be used to style the headers used on your site's pages. By using H1 and H2 tags, for instance, instead of font tags, you are showing the search engines which words are more important (another tip--use keywords in your titles).
By using a style sheet, you can control how the different header tags (H1, H2, etc.) appear to your visitors. Besides, in HTML5, you aren't allowed to use HTML for markup--that's what CSS was designed for!