What is meaning of css. It is mostly use in html. but why.
Suggest you Google it and read up on it
Now a day answer like that is very easy find just by using a search engine like Google as irishman suggested above.
I usually go to sites like wikipedia.org for general answer:
For a more detail answer then I look for sites that are focusing on the topic of interest. For example, for CSS and web design, there is a section for that in about.com:
Members here may suggest other valuable resources as well as answer to your question directly. There is a bunch of members here that are very knowledgeable of topic like this.
CSS stands for Cascading Style Sheets. In addition to the links tom8 suggested, you could look at the SitePoint CSS Reference for more information.