Hi Mike,
Thanks for using Syncfusion products.
Your requirement of customizing the css for both button and
ribbon control can be achieved with Essential Studio latest version v10.2.0.75.
We have provided CustomCss support for button control since v10.2.0.56. So
could you please let us know the version details of Essential Studio you are
using? Kindly upgrade to the latest version which has the support for your
requirement.
Please let us know if you have any other concerns.
Regards,
Meena