Under the “Small, but useful” section on https://ubuntubudgie.org/ there is that “Learn more” button, which leads to the code view of budgie-applets.html.
Not sure if you wanted to use the HTML preview (which shows an empty page, since some resources are blocked by my browser (Firefox) due to MIME type mismatch) or a different link?
Or just rename the button to “Learn HTML” 