highchart 对于顶端刻度丢失问题

 title: {
     text: '',
     align: 'center'
 },
 labels: {
     overflow: 'justify',
     formatter: function () {
         return this.value
     },
     style: {
         color: 'rgba(0, 0, 0,0)',
         fontSize:'0.6rem',
         fontFamily:'微软雅黑'
     }
 },
 stackLabels: {
     allowOverlap: false,
     style: {
         color: 'black'
     },
     enabled: true
 }

在fontSize:'0.6rem'中不要设置em。会导致：