Advantages of using CSS in your website

CSS Stands for Cascading Style Sheets. CSS are used to separate the stylist elements of a page such as colour and fonts from the content of the page such as header tags and paragraphs. You can learn CSS from easy W3schools.com tutorials.

Advantages of using CSS in your website:

Full control of page structure
CSS allows you to display your web page according to W3c HTML standards without making any compromise with the actual look of the page.

Google gives value to the web pages that are well organized, though its designers that choose to ignore standards and guidelines, because incorrectly they believe standards lead to bland pages. Using Cascading Style Sheets (CSS), designers can make pages with good lookup, which can be changed easily any time.

Smaller file sizes
By separating styles from HTML page and putting it into a standalone CSS style sheet (.css file), designer can reduce the of code in your web pages. Pages with less code have smaller file sizes and Google and other major search engines prefers pages with smaller file sizes.

Apart from that Google doesn't define the actual page size of the web page, but community of search engine optimizers believe that the size of a web page is not be greater than 100KB.

Hide content from browsers while it still gets picked up by Google

CSS plays an important role when you need to hide specific code or content from web browser but not from the search engines. For example you may have some content like site navigation, that you only want to appear in print, or on the screen .The advantage of CSS is that search Engine will still crawl and index all of the content of your site navigation.