Rounded buttons for UI

Hi,

I noticed some new scripts floating around on the internet that have round-cornered buttons, but I can't seem to find how to do it. (This is for both buttons and iconButtons)

I think this was introduced in CC 2017, is there an updated documentation? I feel I'm working with antiques, the ones I have are 2 PDFs named :

- After-Effects-CS6-Scripting-Guide.pdf

- javascript_tools_guide.pdf

Thanks.