Sets the border width of the container.
The border width of a container is the amount of space to leave around the outside of the container. The only exception to this is Window; because toplevel windows can’t leave space outside, they leave the space inside. The border is added on all sides of the container. To add space to only one side, use a specific margin property on the child widget, for example margin_top.
amount of blank space to leave outside the container. Valid values are in the range 0-65535 pixels.