relativeChildPosition method
Converts a double value to a child-size-relative PositionUnit.
Creates a position unit that is proportional to a child element's size.
For example, 0.5.relativeChildPosition() creates a position that is 50%
of the child's dimension along the relevant axis.
The optional key parameter can be used to reference a specific child
element when multiple children are present.
This is equivalent to PositionUnit.childSize(key) * this.position.
Implementation
PositionUnit relativeChildPosition([Key? key]) =>
PositionUnit.childSize(key) * position;