Css property in form > button

Inside the form, buttons has a css property. I guess this should set my custom class to the rendered button, but this is not working. See an example here

I apologize for the delay.
The problem in the docs is confirmed.
We’ll fix that error in the docs in the future.
Unfortunately it is not available to assign the custom classes to the form button.

Thanks. Could be another error in docs:
In Form > List of Controls > DatePicker the “value” property appears two times.

Confirmed.
Thank you for your note.