CSS (Cascading Style Sheets) is a way that the computer can go through your website more quickly. As may or may not know, browsers love websites that are heavily reliant on CSS rather than heavily relied on HTML because it makes them more “light weight.”
Most people, however, don’t know that using your CSS perfectly can also help with your rankings in the search engines. The more light weight your websites are the faster the bots and spiders can read them, and search engines are very friendly towards slow moving websites with bulky and unattractive coding.
Since the bots and spiders can read them faster, this in turn means that your websites will get indexed faster. Being indexed in the search engines is the first major step to rising up in the search engines as it is the first step to even being visible in the search engines!
This may seem very unsubstantial at first, but having great CSS in all aspects of your website (especially if you have a whole network of websites) will really positively affect your SEO in the long run, and SEO is all about the long run.
Every time you upload a new article, or a new page, it will be indexed faster, and if you are uploading hundreds of articles or pages each year, the effect of great CSS can really help increase the “age” of your website by increasing the speed of when it is able to show up in the SERPs.