What is the difference between W3.CSS and CSS?

Question :

What is the difference between W3.CSS and CSS?

CSS: It is cascading style sheet used for style the web pages, with help of css, you can style the web pages, websites, etc. CSS is a modern framework with built in responsiveness.

W3.CSS: It is CSS framework, build for responsive design, like bootstrap, that means you create responsive websites with help of W3.CSS. It is very easy to learn and quite fast for mobile application. 

It has in-built mobile responsive feature which helps you to make mobile responsive.