anchor.diff:      switch(_squareState) {
         case SquareState.flagged:
           return 'orange';
  -      case SquareState.revealed:
  -        return 'white';
         case SquareState.mine:
           return 'red';
         case SquareState.safe:
           return 'green';
  -      case SquareState.hidden:
  -        return '#6666CC';
         default:
  -        throw 'not supported';
  +        throw 'not supported - $_squareState';
       }
     }
   }
  
positive.code:       ctx.strokeRect(0.5, 0.5, width, height, 1);
      }
  
      if(_squareState == SquareState.revealed) {
        final adjCount = _adjacentCount;
        if(adjCount > 0) {
          final halfSize = _size ~/ 2;
          ctx.textBaseline = 'middle';
          ctx.font = '${halfSize}px Helvetica';
          ctx.fillStyle = 'black';
          ctx.textAlign = 'center';
          ctx.fillText(adjCount.toString(), halfSize, halfSize, _size);
        }
      }
  
    }
  
  
negative.code: class SquareElement extends PElement {
    static const int _size = 80;
    static const String _textureName = "balloon.png";
    static const List<String> _numberMap = const["game_board_center",
                                                 "number_one", "number_two",
                                                 "number_three", "number_four",
                                                 "number_five", "number_six",
                                                 "number_seven", "number_eight"];
  
    final int x, y;
  
    SquareElement(this.x, this.y) : super(_size, _size) {
  