I want to widen the popup window in Kendo UI grid. So that also the elements in it fill the window.
In the answer How do I Change window size on kendo grid editor template? only the window is made wider, but not also the elements contained in it.
Simple provide the width in your grid definition: https://docs.telerik.com/kendo-ui/api/javascript/ui/grid/configuration/editable.window or see https://stackoverflow.com/a/30778406/4944034 for a practical example.