Add static text labels

Add static text labels to the center of features. This is not the same as fitting labels dynamically. The labels will collide as you zoom out.
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<html>
  <head>
    <meta charset="utf-8" />
    <title>Add static text labels</title>
    <meta name="viewport" content="initial-scale=1, maximum-scale=1, user-scalable=no" />
    <link rel="stylesheet" href="https://unpkg.com/leaflet@1.9.4/dist/leaflet.css" crossorigin="" />
    <script src="https://unpkg.com/leaflet@1.9.4/dist/leaflet.js" crossorigin=""></script>

    <!-- Load Esri Leaflet from CDN -->
    <script src="https://unpkg.com/esri-leaflet@3.0.10/dist/esri-leaflet.js"></script>

    <!-- Load Esri Leaflet Vector from CDN -->
    <script src="https://unpkg.com/esri-leaflet-vector@4.2.5/dist/esri-leaflet-vector.js" crossorigin=""></script>
    <script>
    </script>
    <style>
      html,
      body,
      #map {
        padding: 0;
        margin: 0;
        height: 100%;
        width: 100%;
        font-family: Arial, Helvetica, sans-serif;
        font-size: 14px;
        color: #323232;
      }
    </style>
  </head>
  <body>
    <style>
      .label {
        font-weight: 700;
        text-transform: uppercase;
        text-align: center;
        margin-top: -1em;
      }

      .label div {
        position: relative;
        left: -50%;
        top: 10px;
        text-shadow: 0px 2px 1px rgba(255, 255, 255, 0.85);
      }
    </style>

    <div id="map"></div>
    <script>
      const accessToken = "YOUR_ACCESS_TOKEN";

      const map = L.map("map").setView([37.428, -121.978], 9);

      L.esri.Vector.vectorBasemapLayer("arcgis/oceans/base", {
        token: accessToken
      }).addTo(map);

      const earthquakes = L.esri
        .featureLayer({
          url: "https://sampleserver6.arcgisonline.com/arcgis/rest/services/Earthquakes_Since1970/MapServer/0"
        })
        .addTo(map);

      const labels = {};

      earthquakes.on("createfeature", function (e) {
        const id = e.feature.id;
        const feature = earthquakes.getFeature(id);
        const center = feature.getLatLng();
        const label = L.marker(center, {
          icon: L.divIcon({
            iconSize: null,
            className: "label",
            html: "<div>" + e.feature.properties.name + "</div>"
          })
        }).addTo(map);
        labels[id] = label;
      });

      earthquakes.on("addfeature", function (e) {
        const label = labels[e.feature.id];
        if (label) {
          label.addTo(map);
        }
      });

      earthquakes.on("removefeature", function (e) {
        const label = labels[e.feature.id];
        if (label) {
          map.removeLayer(label);
        }
      });
    </script>
  </body>
</html>