internal override void Undo()
 {
     TargetDrawing?.ChangeLineThickness(prevLineThickness);
 }
 internal override void Redo()
 {
     TargetDrawing?.ChangeLineThickness(lineThickness);
 }
 public override bool Execute()
 {
     TargetDrawing?.ChangeLineThickness(lineThickness);
     return(true);
 }