I've seen a couple examples of Space Planners that have the units symbolized based on how many occupants are currently assigned to it, as in these examples from CloudPoint and CERN below. The images link to the videos I pulled these pictures from if you want to check them out.


However I cannot seem to figure out how they achieved this. I see an option in the web map to adjust transparency based on a field, which I can then set to the Capacity field, but that's not quite what I'm looking for; the capacity will always stay the same regardless of occupants assigned. I cannot seem to find a field in the units layer that updates when assigning occupants.
Does anyone know how this was achieved? Or have any ideas of things to try?
Thanks!