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>
<div id="map"></div>

CSS

#map { position: absolute;top:0;bottom:0;left:0;right:0; }

JavaScript

var map = L.map('map');
var gj = L.geoJson({
    "type": "Polygon",
    "coordinates": [[
        [11, 57],
        [12, 57],
        [12, 58],
        [11, 58]
    ]]
}).addTo(map);

map.fitBounds(gj.getBounds());