W3.CSS is a free to use CSS framework with features of responsiveness whereas W3.JS is a javascript library
W3.CSS is based on standard CSS therefore easier to learn and use. It supports responsiveness and provides CSS equality across all browsers and all devices.
W3.JS is smaller and faster than other JavaScript libraries. It is designed to speed up application development.
W3.CSS classes start with “w3-propertyname” and W3.JS selects and performs action using “w3.action(selector)”