echarts 渐变色

itemStyle: {
    color: new echarts.graphic.LinearGradient(
      0, 0, 0, 1,
      [
        { offset: 0, color: "#ffd077" },
        { offset: 0.3, color: "#fcbe49" },
        { offset: 0.6, color: "#c3bf1d" },
        { offset: 1, color: "#777a2a" }
      ]
    )
  }