回答

echarts.init的第二个参数设置为dark，代码如下：

<!DOCTYPE html>
<html>

<head>
    <meta charset="utf-8">
    <script type="text/javascript" src="//repo.bfw.wiki/bfwrepo/js/echarts.js"></script>
</head>

<body>
    <div id="myChart" style="width: 800px; height: 600px;"></div>

    <script type="text/javascript">
        var chart = echarts.init(document.getElementById('myChart'),"dark");
var option = {
  legend: {
    top: 'bottom'
  },
  toolbox: {
    show: true,
    feature: {
      mark: { show: true },
      dataView: { show: true, readOnly: false },
      restore: { show: true },
      saveAsImage: { show: true }
    }
  },
  series: [
    {
      name: 'Nightingale Chart',
      type: 'pie',
      radius: [50, 250],
      center: ['50%', '50%'],
      roseType: 'area',
      itemStyle: {
        borderRadius: 8
      },
      data: [
        { value: 40, name: 'rose 1' },
        { value: 38, name: 'rose 2' },
        { value: 32, name: 'rose 3' },
        { value: 30, name: 'rose 4' },
        { value: 28, name: 'rose 5' },
        { value: 26, name: 'rose 6' },
        { value: 22, name: 'rose 7' },
        { value: 18, name: 'rose 8' }
      ]
    }
  ]
};

       
        chart.setOption(option, true);
    </script>
</body>

</html>