series: [{
 name: '数量',
 type: 'bar',
 data: yAxis,
 itemStyle: {//渐变色
  color: new this.$echarts.graphic.LinearGradient(
      0, 0, 0, 1,
    [
     {offset: 0, color: '#f00'}, 
     {offset: 1, color: '#00f'}
    ]
  ), 
  barBorderRadius: [45, 45, 0, 0] //圆角
},