anchor.diff:      return new SnackBar(
         key: key ?? fallbackKey,
         content: content,
  +      backgroundColor: backgroundColor,
         action: action,
         duration: duration,
         animation: newAnimation
  
positive.code:             },
              child: new Material(
                elevation: 6,
                color: _kSnackBackground,
                child: new Theme(
                  data: darkTheme,
                  child: new FadeTransition(
  
negative.code:   ///
    /// Typically a [Text] widget.
    final Widget content;
  
    /// The Snackbar's background color. By default the color is dark grey.
    final Color backgroundColor;
  
    /// (optional) An action that the user can take based on the snack bar.
    ///
  