W3.CSS was released in 2017.
The latest version is W3.CSS 4.15 December 2020.
The latest version can be downloaded from W3.CSS Downloads.
Version 4 is the default style sheet used in all the pages of W3Schools.
W3.CSS - Pro
W3.CSS comes with a professional version: w3pro.css.
The pro version is smaller and faster because it has no colors defined.
The pro version is designed for using themes or other color classes supplied by the developer.
The pro version can be downloaded from: https://www.w3schools.com/w3css/4/w3pro.css
W3.CSS Pro Colors
With W3.CSS pro you can define your own colors:
<meta name="viewport" content="width=device-width, initial-scale=1">
<link rel="stylesheet" href="https://www.w3schools.com/w3css/4/w3pro.css">
<!-- Colors here -->
<!-- Content here -->
You can define your colors inline with a <style> tag:
Or you can load your own themes:
Or you can load your color libraries: