Hi Rory,
We are not sure what you mean by "
style settings disappear. Images, widths, etc". I just checked the css file Calendar.Outlook.css and it seems perfectly fine. Note that DatePicker is a composite control that uses both RadCalendar and RadDateInput, so you should modify the Input.Outlook.css as well. More info on using the default skins as base for custom skins is available here.
Kind regards,
Steve
the Telerik team