Hi Thanvir,
Thanks for using Syncfusion Products.
If your intention is to set themes for your application means, you need to set the theme and color scheme of each control in your application. There is no other way to set a theme for whole application.
Please refer the attached sample.
http://websamples.syncfusion.com/samples/Tools.Windows/F63796/main.htmThe above sample which illustrates how to set a theme and color scheme for the Form and the controls in the application.
Please let me know if you have any more queries.
Regards,
Rashidha.