In your HTML document, include the CSS and JavaScript API files.
HTML
<script src="https://api.geoconcept.com/EU/GCW/geoconcept-web/combo?babel-external-helpers-min.js&yui-min.js&gcui-loader-min.js&webjars-requires.js&loader-init-min.js"></script> <script src="https://cdn.rawgit.com/openlayers/openlayers.github.io/master/en/v5.3.0/build/ol.js"></script> <link rel="stylesheet" href="https://openlayers.org/en/v5.3.0/css/ol.css" type="text/css" /> <script src="https://api.geoconcept.com/EU/GCW/geoconcept-web/combo?gcui-htc6/htc.js"></script>
