What is "w3.css"
Download
Download or direct link: http://www.w3schools.com/lib/w3.css
Does not use licenses
W3.CSS is totally free to use without the need for licenses.
How to use
Just copy the link above and put it on your page like this:
<!DOCTYPE html>
<html>
<title>My Web</title>
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="http://www.w3schools.com/lib/w3.css">
Or you can download the w3.css to your local server or machine and point directly:
<link rel="stylesheet" href="css/w3.css">
Or:
<link rel="stylesheet" href="assets/css/w3.css">
Sources: