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：