版权声明：@copyright by taorui https://blog.csdn.net/weixin_42541498/article/details/82968377
像这样的tooltip可以借助tooltip的formatter来实现，背景图片用extraCssText选项来实现
extraCssText: "width:283px;height:274px;background: url(scene/assets/hebei/hb-family-monitor/OLT设备监控-tooltip.png) no-repeat;",