JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://code.highcharts.com/js/highcharts.js"></script>

<strong>Question:</strong> Can we adjust the line-height of axis labels in Highcharts when using CSS styled mode?

<div id="container"></div>

<p><strong>Using CSS styled branch:</strong> http://code.highcharts.com/js/highcharts.js</p>
<p><strong>With CSS:</strong> http://code.highcharts.com/css/highcharts.css</p>

SCSS

@import 'https://code.highcharts.com/css/highcharts.css';

body {
  max-width: 640px;
  margin: 2em auto;
  text-align: center;
  font-family: courier;
  * {
    font-family: courier;
  }
}

#container {
  min-width: 310px; 
  max-width: 500px; 
  height: 200px; 
  margin: 0 auto
}

.highcharts-xaxis-labels {
  font-size: 15px;
  // line-height: 0.5 !important; // Has no effect on line height
  // text-overflow: none; // has no effect on automatic ellipsizing 

  text:nth-child(odd){ fill: blue; }
  text:nth-child(even){ fill: red; }
  
}

JavaScript

var H = Highcharts;
H.wrap(H.Tick.prototype, 'addLabel', function (p) {
  p.call(this);
  
  const label = this.label;
  const labelOptions = this.axis.options.labels;
  
  if (label) {
    label.css({
      lineHeight: labelOptions.style.lineHeight
    })
  }
})

Highcharts.chart('container', {
    chart: { type: 'bar' },
    title: { text: null },
    legend: { enabled: false},
    credits: { enabled: false },
    xAxis: {
        labels: {
          style: { 
            textOverflow: 'none', // To disable automatic ellipsizing, per https://github.com/highcharts/highcharts/issues/3941
            // lineHeight: '0.5' // Has no effect
            lineHeight: 12
          }
        },
        categories: [
          'Sweden', 
          'Federal Democratic Republic of Ethiopia', 
          'Finland',
          'United Kingdom of Great Britain and Northern Ireland', 
          'Oceania'],
        title: {
            text: null
        }
    },
    yAxis: {
        visible: false,
        labels: {
            overflow: 'justify'
        }
    },
    series: [{
        name: 'Year 1800',
        data: [107, 313, 635, 203, 262]
    }]
});