JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.7.3/leaflet.css">
<script src="http://cdn.leafletjs.com/leaflet-0.7.3/leaflet.js"></script>
<script src="http://cdn-geoweb.s3.amazonaws.com/esri-leaflet/0.0.1-beta.5/esri-leaflet.js"></script>
<div id="map"></div>

CSS

html, body, #map {
  height: 100%;
  width: 100%;
  margin: 0;
  padding: 0;
}

JavaScript

var map = new L.Map("map").setView([39.891431,-104.944668], 12);

L.esri.basemapLayer("Topographic").addTo(map);

var featureId = 126;
var url = "http://services.arcgis.com/IamIM3RJ5xHykalK/ArcGIS/rest/services/Webmap_County/FeatureServer/0";

function drawFeature(error, features, response){
    var geojson = L.esri.Util.arcgisToGeojson(response.features[0]);
    L.geoJson(geojson).addTo(map);
}

//L.esri.Tasks.query(url).where("FID='"+featureId+"'").run(drawFeature);
L.esri.Tasks.query(url).where("FID='"+featureId+"'").simplify(map, 0.8).run(drawFeature);