echarts 下钻 返回设成按钮的样式

graphic: [
          {
            type: 'group',
            right: 0,
            top: 0,
            children: [
              {
                type: 'rect',
                z: 100,
                left: 'center',
                top: 'middle',
                shape: {
                   50,
                  height: 25
                },
                style: {
                  fill: '#fff',
                  stroke: '#51A3E6',
                  lineWidth: 1,
                  shadowBlur: 8,
                  shadowOffsetX: 3,
                  shadowOffsetY: 3,
                  shadowColor: 'rgba(81,163,230,0.2)'
                }
              },
              {
                type: 'text',
                z: 100,
                left: 'center',
                top: 'middle',
                style: {
                  fill: '#51A3E6',
                   220,
                  overflow: 'break',
                  text: '返回',
                  font: '14px Microsoft YaHei'
                }
              }
            ]
          }
        ]