How to customize the Map Cluster icon (Leaflet) via custom.css?

Hello everyone,

I am trying to customize the default green circle cluster icon on the map. Because I have multiple devices in the same location, I need to keep clustering enabled, but I would like the cluster icon to look like a standard map pin (with a shadow) that just has the number of grouped devices on it.

I tried using custom.css to override the Leaflet classes (.marker-cluster, etc.) and loaded a different background image. However, it seems that the map view completely ignores custom.css (even after clearing views/cache and using incognito mode).

Is there a supported way to change the cluster icon or inject custom CSS into the map view without modifying the core system files?

Thanks in advance!