margin property
final
The empty space that surrounds the tooltip.
Defines the tooltip's outer Container.margin. By default, a long tooltip will span the width of its window. If long enough, a tooltip might also span the window's height. This property allows one to define how much space the tooltip must be inset from the edges of their display window.
If this property is null, then TooltipThemeData.margin is used. If TooltipThemeData.margin is also null, the default margin is 0.0 logical pixels on all sides.
Implementation
final EdgeInsetsGeometry? margin;