JSFiddle - React, Tailwind, and code Playground

HTML

<script src="https://cdn.jsdelivr.net/leaflet/0.7.3/leaflet.js"></script>
<script src="https://cdn.jsdelivr.net/leaflet.esri/1.0.0/esri-leaflet.js"></script>
<link rel="stylesheet" href="https://cdn.jsdelivr.net/leaflet/0.7.3/leaflet.css">
<title>Map</title>
<div id="map" style="width:400px;height:400px;"></div>

JavaScript

(function() {
    var map = L.map('map').setView([54.296500, -2.209221], 5);
    L.esri.basemapLayer('Oceans').addTo(map);

    var popup = L.popup();

})();