This is the CDN of Studio Carbon. How to use this CDN:

 - Browse a repository and select a version.
   w3css > 4.13 > w3.css

 - Click the title on the preview panel to select the whole URL.
 - Copy URL and embed in your website!

Example embeds:

<link rel="stylesheet" href="url/to/css/file">
<script src="url/to/javascript/file"></script>