JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.highcharts.com/highcharts.js"></script>
<script src="https://code.highcharts.com/modules/data.js"></script>
<script src="https://code.highcharts.com/modules/accessibility.js"></script>
<script src="/js/dark-unica.js"></script>
<script>
Highcharts.getJSON(
    'https://www.pogodakrotoszyn.pl/tempdata.json',
    function(data) {
        var minTemp = Math.min(...data.temp);
        var maxTemp = Math.max(...data.temp);

        Highcharts.chart('temperatura', {
            chart: {
                backgroundColor: 'rgba(40,40,40,1)',
                events: {
                    load: function() {
                        const chart = this;
                        this.series.forEach(series => {
                            const min = series.dataMin,
                                  max = series.dataMax;

                            series.points.forEach(point => {
                                if (point.y === min || point.y === max) {
                                    point.update({
                                        dataLabels: {
                                            enabled: true,
                                            formatter: function() {
                                                return this.y + '°C';
                                            },
                                            style: {
                                                color: 'white',
                                                fontSize: '16px'
                                            }
                                        }
                                    });
                                }
                            });
                        });
                    }
                }
            },
            title: {
                text: ' '
            },
            xAxis: {
                type: 'datetime',
                labels: {
                    style: {
                        color: 'white'
 ...