如何更改仪表图中值的字体大小(Plotly.js)

<script src="https://cdn.plot.ly/plotly-latest.min.js"></script>

<div id="gauge"></div>

var data = [
  {
    type: "indicator",
    mode: "gauge+number",
    value: 80,
    gauge: {
      axis: { range: [null, 100] },
      bar: { color: "darkblue" },
      bgcolor: "white",
      borderwidth: 2,
      bordercolor: "gray",
      steps: [
        { range: [0, 50], color: "lightgray" },
        { range: [50, 100], color: "gray" }
      ],
      threshold: {
        line: { color: "red", width: 4 },
        thickness: 0.75,
        value: 90
      }
    }
  }
];

var layout = {
  font: { size: 18 } // 设置字体大小为18
};

Plotly.newPlot("gauge", data, layout);