Highcharts yAxis Categories Not Aligning Closest to Axis Line

I want to adjust the positioning of the yAxis categories. Specifically, I want the first category (“Low”) to start right at the xAxis line without any padding or space before it.

Highcharts.chart("container", {
  chart: {
    type: "line",
  },
  title: {
    text: "Monthly Data",
  },
  xAxis: {},
  yAxis: [{
      opposite: true,
      categories: ["Low", "Meduim", "High"],
      title: {
        text: "Severity",
      },
    },
    {
      title: {
        text: "Measurment",
      },
    },
  ],
  series: [{
      yAxis: 0,
      name: "Severity",
      data: [0, 1, 0, 1, 0, 0, 0, 1, 1],
    },
    {
      yAxis: 1,
      name: "Measurment",
      data: [0, 5, 20, 5, 2, 5, 1],
    },
  ],
  tooltip: {
    shared: true,
    valueSuffix: "",
  },
})
<script src="https://code.jquery.com/jquery-3.1.1.min.js"></script>
<script src="https://code.highcharts.com/highcharts.js"></script>
<script src="https://code.highcharts.com/modules/exporting.js"></script>

<div id="container" style="height: 300px; margin-top: 1em"></div>
<button id="button">Export chart</button>