How to Intercept page scroll event

Development
3

Got it, for anyone in the same case you need to add the following script into the body (via the admin interface)

<script type="text/javascript">
    Discourse.initializer({
      name: 'custom-header',

      initialize: function(application) {
        
        application.registrations['app-events:main']
            .on('header:show-topic', function(e){ 
                $('#top-navbar').css('zIndex',0) 
            })
            .on('header:hide-topic', function(e){ 
                $('#top-navbar').css('zIndex',1001) 
            })
      }
   });
</script>