finally found it
Code:
<Mapping ArtAssetID="silver_border_bottom_left" FileName="..\Panels\panelBorderBottomLeftCorner.tga" />
<Mapping ArtAssetID="silver_border_bottom_right" FileName="..\Panels\panelBorderBottomRightCorner.tga" />
<Mapping ArtAssetID="silver_border_top_left" FileName="..\Panels\panelBorderTopLeftCorner.tga" />
<Mapping ArtAssetID="silver_border_top_right" FileName="..\Panels\panelBorderTopRightCorner.tga" />