62f31996_L_View_Graphics___Face_Effects__Description
[Effect] round [Arguments] pair! tuple! integer! integer! [Description] 
Generate tab buttons with rounded corners. The optional arguments are: a pair! that specifies the edge to round, a tuple! that is used as an edge color, an integer! that indicates the radius of the curves, and an integer! that controls the thickness of the edge.
REBOL/View Graphics - Face Effects
Description