Hi Milos,
We suspect that you have not referred CSS file(ej.web.all.min.css) in your application. So only the reported issue occurs. Also please define the script template in index.html instead of welcome.html file. Could you please check in the below sample? Still if you have an issue, please provide us more details such as browser version, console error in browser, screenshot of an issue.
Code example:
Index.html
<link rel='nofollow' href="//cdn.syncfusion.com/15.1.0.37/js/web/flat-azure/ej.web.all.min.css" rel="stylesheet" />
<script id="connectionOrganizationTemplateId" type="text/x-jsrender">
<div class="node-content" data-entityid="{{:id}}" data-entitytype="{{:entity}}" style="border-color: {{:color}}">
<div class="node-image {{:spriteCssClass}}"></div>
<p class="node-text">{{:displayName}}</p>
</div>
</script>
Regards,
Shyam G