flex/templates/partial/ggst.html

{% if GOOGLE_GLOBAL_SITE_TAG %}
<script async src="https://www.googletagmanager.com/gtag/js?id={{ GOOGLE_GLOBAL_SITE_TAG }}"></script>
<script>
  window.dataLayer = window.dataLayer || [];
  function gtag(){dataLayer.push(arguments);}
  gtag('js', new Date());

  gtag('config', '{{ GOOGLE_GLOBAL_SITE_TAG }}');
</script>
{% endif %}