GridViewCell border style

[Danilo]

Hello, I'm having a problem while trying to apply a style on a GridViewCell. I want to define the BorderThickness of the cell. My problem is that: I have a ColumnGroup with two columns and I want that just the borders of the ColumnGroup stay on screen. With that I will have the ColumnGroups setted apart, but not the Columns. 
To accomplish that I'm trying to set on the right Column just the right border, and on the left Column just the left border. Therefore it's not working. The Style that I'm using is not working.

Best Regards,

Danilo Rufino