I have a CalendarDatePicker
control on my UWP app. I am not able to increase the size of the font of the date that is selected using the FontSize
a
You can check the properties of the control using Live Visual Tree tool, in your case you want to change the size of the internal TextBlock:
You can modify the TextBlock font size in a copy of the default style https://msdn.microsoft.com/en-us/library/windows/apps/mt299110.aspx
As you can see, it is hardcoded to 15 in the default template: