Considering the template structure of GridViewRow you cannot change its indicator with a simple style.
You need to edit the template of GridViewRow to achieve the desired result as it is shown at the attached example. As far as I can understand you cannot edit the template of GridViewRow by some reason.
Can you please try the approach below and let me know what happens:
1.Find in Assets
library a single GridViewRow.
2.Drag it onto the Artboard
, right click on it and choose the option Edit Template -> Edit a copy
You may use the same approach for any other GridView part.
the Telerik team
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