JSFiddle - React, Tailwind, and code Playground

HTML

<link rel="stylesheet" href="http://cdn.leafletjs.com/leaflet-0.5/leaflet.css">
<script src="http://cdn.leafletjs.com/leaflet-0.5/leaflet.js"></script>
<div id="map"></div>

CSS

#map {
    height: 500px
}

JavaScript

var poly = [{
    "type": "Polygon",
    "properties": {},
    "coordinates": [
        [9.506612, 54.791087],
        [9.506406, 54.790930],
        [9.506134, 54.790762],
        [9.505918, 54.790525],
        [9.505863, 54.790251],
        [9.505593, 54.790048],
        [9.505033, 54.789785],
        [9.504743, 54.789625],
        [9.506612, 54.791087]]
}];

var map = L.map('map').setView([54.78252, 9.437509], 13);

L.tileLayer('http://otile1.mqcdn.com/tiles/1.0.0/osm/{z}/{x}/{y}.png', {
    maxZoom: 18
}).addTo(map);

var myStyle = {
    "color": "#ff0000",
    "weight": 5
};

L.geoJson(poly, {style: myStyle}).addTo(map);