anchor.diff:    Widget build(BuildContext context) {
       final Widget bottomSheet = Material(
         key: _childKey,
  +      elevation: widget.elevation,
         child: widget.builder(context),
       );
       return !widget.enableDrag ? bottomSheet : GestureDetector(
  
positive.code:   ///
    /// Default is true.
    final bool enableDrag;
  
    @override
    _BottomSheetState createState() => _BottomSheetState();
  
negative.code:     Key key,
      this.animationController,
      this.enableDrag = true,
      this.elevation = 0.0,
      @required this.onClosing,
      @required this.builder
    }) : assert(enableDrag != null),
         assert(onClosing != null),
         assert(builder != null),
         assert(elevation != null),
         super(key: key);
  
    /// The animation that controls the bottom sheet's position.
  