message: Add chart export background
diff: @@ -289,6 +289,11 @@ export class ChartWidget implements IDestroyable {
  }
  }
  });
  + // Set chart background
  + ctx.globalCompositeOperation = 'destination-over';
  + ctx.fillStyle = this._options.layout.backgroundColor;
  + ctx.fillRect(0, 0, targetCanvas.width, targetCanvas.height);
  + ctx.globalCompositeOperation = 'source-over';
  return targetCanvas;
  }
  