You can see some additional Chart.js examples on the charts samples page.
icon outputs an SVG icon and takes the icon name as its only parameter. The icon is scaled to match the current text size.
Example:
{{< icon "github" >}}
-Output: +
Output: +
Icons are populated using Hugo pipelines which makes them very flexible. Congo ships with a default set of icons for social, email, and generic links. If you want to add your own icons, you can simply place them in /assets/icons/ and reference them using the icon shortcode passing in the icon’s filename (without the .svg. extension).
The examples below are a small selection taken from the official Chart.js docs. You can also view the page source on GitHub to see the markup.