Where to find native/base Icon Theme json file

I have a requirement to use a Gray or Black check mark icon under the Conditional Formating->Icons selection option.

I have watched Reid Haven's videoes on how to add new icons but what I find is that all I need to do is change the existing icon's color. See below link

https://powerbi.tips/product/theme-file-with-icon-set/

Does any one know where I can find the native/base json icon code that Power BI would use out of the box. Once I get the base set I am sure I can figure out how to change the color.

Thx, Mark