Modify the look for the GridFilterBar custom filter popup

I would like to modify the form that pops up when the user click on the (custom)item in a GridFilterBar instance wired to a GridDataBoundGrid object. Example of what I want to change: - The BackColor property; - Remove the second textbox in some cases; - and more... What do I need to override/replace/call to be able to perform these kind of changes? Thank you!

SyncFusion_GridFilterBar_CustomFilter_Popup.zip

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