WPF ： The ItemsControl border has extra lines appearing.

I am using ItemsControl with WrapPanel as the panel and have set a border for the ItemsControl. How can I make the border apply only to the content area? Right now, there is extra space beyond the content area. <Setter Property="ItemsPanel"> <Setter.Value> <ItemsPanelTemplate> <WrapPanel Orientation="Horizontal" IsItemsHost="True" /> </ItemsPanelTemplate> </Setter.Value> </Setter>