高图的CSS实现不工作

我试图建立一个callout并通过CSS格式化callout。由于某些原因，css的实现不能正常工作。

<script src="https://code.highcharts.com/highcharts.js"></script>
<script src="https://code.highcharts.com/modules/exporting.js"></script>
<div id="container" style="min-width: 310px; height: 400px; margin: 0 auto"></div>

div.callout {
  height: 20px;
  width: 100px;
  /*float: left;*/
  z-index: 1;
}
div.callout {
  background-color: #444;
  background-image: -moz-linear-gradient(top, #444, #444);
  position: relative;
  color: #ccc;
  padding: 10px;
  border-radius: 3px;
  box-shadow: 0px 0px 20px #999;
  margin: 25px;
  min-height: 20px;
  border: 1px solid #333;
  text-shadow: 0 0 1px #000;
  /*box-shadow: 0 1px 0 rgba(255, 255, 255, 0.2) inset;*/
}
.callout::before {
  content: "";
  width: 0px;
  height: 0px;
  border: 0.8em solid transparent;
  position: absolute;
}
.callout.top::before {
  left: 45%;
  bottom: -20px;
  border-top: 11px solid #444;
}
.callout.bottom::before {
  left: 45%;
  top: -20px;
  border-bottom: 10px solid #444;
}
.callout.left::before {
  right: -20px;
  top: 40%;
  border-left: 10px solid #444;
}
.callout.right::before {
  left: -20px;
  top: 40%;
  border-right: 10px solid #444;
}
.callout.top-left::before {
  left: 7px;
  bottom: -20px;
  border-top: 10px solid #444;
}
.callout.top-right::before {
  right: 7px;
  bottom: -20px;
  border-top: 10px solid #444;
}

JS:

$(function () {
    $('#container').highcharts({
        title: {
            text: 'Monthly Average Temperature',
            x: -20 //center
        },
        subtitle: {
            text: 'Source: WorldClimate.com',
            x: -20
        },
        xAxis: {
            categories: ['Jan', 'Feb', 'Mar', 'Apr', 'May', 'Jun',
                'Jul', 'Aug', 'Sep', 'Oct', 'Nov', 'Dec']
        },
        yAxis: {
            title: {
                text: 'Temperature (°C)'
            },
            plotLines: [{
                value: 0,
                width: 1,
                color: '#808080'
            }]
        },
        tooltip: {
            valueSuffix: '°C'
        },
        legend: {
            layout: 'vertical',
            align: 'right',
            verticalAlign: 'middle',
            borderWidth: 0
        },
        series: [{
            name: 'Tokyo',
            data: [7.0, 6.9, 9.5, 14.5, 18.2, 21.5, 25.2, 26.5, 23.3, 18.3, 13.9, 9.6],
        dataLabels: {
                enabled: true,
                align: 'left',
                crop: false,
                style: {
                    fontWeight: 'bold'
                },
                x: 3,
                verticalAlign: 'middle',
                formatter: function() {
            return '<div class="callout" data-name="Jane">This is a test message</div>'; 
          }
            },
        }, {
            name: 'New York',
            data: [-0.2, 0.8, 5.7, 11.3, 17.0, 22.0, 24.8, 24.1, 20.1, 14.1, 8.6, 2.5]
        }, {
            name: 'Berlin',
            data: [-0.9, 0.6, 3.5, 8.4, 13.5, 17.0, 18.6, 17.9, 14.3, 9.0, 3.9, 1.0]
        }, {
            name: 'London',
            data: [3.9, 4.2, 5.7, 8.5, 11.9, 15.2, 17.0, 16.6, 14.2, 10.3, 6.6, 4.8]
        }]
    });
});