The use of Cascading Style Sheets (CSS) helps to define and separate content from presentation and design aspects. This is an important aspect of Web 2.0 website design and proper SEO friendly development. This separation of content and presentation can provide more flexibiltiy and control over presentation characteristics and design and allows for “tableless” website development.
Prior to CSS, basic HTML development was centered around defining content and design repeatedly throughout every page of a site and made editing difficult. CSS gives a site the flexibility to use style sheets throughout the site, repeat them using slight variations in design, and allows for proper Web 2.0 design/development. CSS is optimal for SEO because the separation of design and content allows the spiders to clearly see the content they need to. When the spiders don’t have to filter through design code and can go directly to properly placed unique content, the page will be cached more easily and show results for the important keywords embedded in that content.