anchor.diff:  
   class FloatLayerAction extends OutlinableAction {
     static const FLOAT_PIXEL_SIZE_FACTOR = 0.85;
  +  static const LIGHTER_LINE_COLOR = 'rgba(0,0,0,0.3)';
  +  static const DARKER_LINE_COLOR = 'rgba(255,255,255,0.3)';
   
     final PixelCanvasElement canvas;
     final FloatLayer floatLayer;
  
positive.code:         ctx
              // draw a white cross
              ..beginPath()
              ..strokeStyle = OutlinableAction.DARKER_LINE_COLOR
              ..moveTo(offset.x, offset.y)
              ..lineTo(offset.x + size, offset.y + size)
              ..moveTo(offset.x + size, offset.y)
  
negative.code: 
        ctx
            ..beginPath()
            ..strokeStyle = DARKER_LINE_COLOR
            ..rect(offset.x + 1, offset.y + 1, size - 2, size - 2)
            ..stroke();
      });
  