Thank you for writing.
If your requirement is to change the color of the vertical scroll bar for the popup, please have a look at the following code snippet:
((FillPrimitive)radDropDownList1.ListElement.VScrollBar.Children).BackColor = Color.Red;
radDropDownList1.ListElement.VScrollBar.ThumbElement.ThumbFill.BackColor = Color.Yellow;
radDropDownList1.ListElement.VScrollBar.ThumbElement.ThumbFill.GradientStyle = GradientStyles.Solid;
radDropDownList1.ListElement.VScrollBar.FirstButton.ButtonFill.BackColor = Color.Green;
radDropDownList1.ListElement.VScrollBar.FirstButton.ButtonFill.GradientStyle = GradientStyles.Solid;
radDropDownList1.ListElement.VScrollBar.SecondButton.ButtonFill.BackColor = Color.Blue;
radDropDownList1.ListElement.VScrollBar.SecondButton.ButtonFill.GradientStyle = GradientStyles.Solid;
If it is not the exact requirement, please specify in detail what is the expected design. Thus, we would be able to suggest a suitable solution.
I hope this information helps. Should you have further questions, I would be glad to help.
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