property Rollist.SelectBorderSize as Long
Specifies a value that indicates the size of the border for selected item.

TypeDescription
Long A long expression that indicates the size of border of the selected item, in pixels.

Use the SelectBorderSize property to define the size of the border of the selected item. Use the ItemBorderSize property to define the size of the border for rest of items.  By default, the SelectBorderSize property is 5 pixels.