Hi Ros,
We have prepared a sample to address your requirement
"To edit Header Style of Calendar"
using HeaderTemplate Property of SfCalendar.
Please find the Sample from below location,
http://www.syncfusion.com/uploads/user/directTrac/116544/115117sfcalendar884831013.zip
Please let us know if you have any queries.
Regards,
Madhan Kumar S