CSS grew originally as a standard for webpage design probably for the most part as a rebellion against the use or possibly the overuse of complex tables in order to force accurate layouts upon a medium which was never intended for such a purpose.
In the early days of the web's development, the battle which raged over who should really control the overall appearance of a webpage or website was pretty much won by the web designers. After all, at the end of the day, users really care most about usability, accessibility and particularly convenience. These users are really not interested in the complexities or problems associated with web design techniques.
The point came where the use of complex table layouts was just really going too far and becoming overtly complex and in general the web design community was becoming uncomfortable with the whole situation not least because maintaining a web page made up of numerous nested tables was something of a nightmare especially as most web designers generally prefer to avoid complexities of code whenever they can. Also web pages containing multiple tables almost invariably result in much longer delays in loading into a browser.
Eventually the World Wide Web Consortium entered the debate. This was a body founded by Tim Berners-Lee to oversee the technical growth of the web. This group quickly realised that separating the content of the site from its framework and appearance would at least be a logical solution and possibly a necessity as this would allow content creators to separately provide what, after all, the visitor wishes to see. It would also enable expert designers and graphic artist to control the artistic or aesthetic elements of the site quite independent from the content.
The resulting creation was CSS.