Thank you for contacting us.
Attached you will find a sample project in which this is illustrated. I have set the Width
property of the Grid which is in the Popup
in order to fix the length of the items, because as you said, it adjusts its length.
Please mind for the "NOTE:" comments which indicate the place where changes have been made.
Let us know if you need further assistance.
All the best,
the Telerik team
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