Hi Sonam,
Thanks for using Syncfusion products.
Your requirement to customize the CSS of DatePicker could be achieved by changing the respective CSS class.
Please refer the following code snippet.
[View]
<%=Html.Syncfusion().DatePicker("myDatePicker").CustomCss("Office2007Blue")
We have created a sample for DatePicker with CustomCSS and the same can be downloaded from the attachment.
Let us know if you have any other concerns.
Regards,
Meena
DatePickerCustom_273c65ed.zip