We are currently working on the help articles about styling the different controls. In the meantime changing the DatePicker might not be so easy. I created a project in blend in which I have changed the skin of the DatePicker (textbox + ToggleButton) and also made the dates smaller, as you wanted.
How did I do this? There is a margin around the ContentPresenter of the DayButton which I decreased by 2 pixels. Then, I modified the MinWidth and MinHeight of the CalendarViews to accommodate the change.
I have attached the completed project.
Normally it is much easier to edit the Calendar and then move the templates/styles to a DatePicker.
Here is a picture of the smaller Calendar and skinned DatePicker.
If you need help with skinning the controls, do come back to us.
the Telerik team
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