For the RadDateTimePicker control, when the EnableEmbeddedSkins property is set to "false," and the Skin property is set to a valid value (e.g. a value that is defined in the appropriate css file) the TimePicker popup uses the embedded stylesheet instead of the custom one supplied by the developer. The DateInput and DatePicker popup, however, use the custom stylesheet. This causes the TimePicker to use the default skin instead of the one specified by the developer.