Zabbix macros, how to access hosts by name, and their items or keys

I have a zabbix 4.2 installation.

I have it currently monitoring a network device via generic SNMP queries with my supplied OIDs. The data is being ingested just fine, graphs are populating as expected.

I would like to make a traffic weathermap, such that the links state the current (or last) bandwidth reading.

Something like this:

But I can't find the macro format that allows what I want to do. Two problems :

1: The link isn't the same as the host. They are different entities. So applying {HOST.NAME} or {HOST.anything} doesn't work. Because the link isn't a HOST. So... HOW do you use a macro that references a host by name? Something like {net-pan-fw.NAME} or {net-pan-fw.HOST} but that doesn't work.

2: How can I reference/call/access a host's member data. The ITEMS or KEYs? Host net-pan-fw has several items, such as net-pan-fw-eth1-310-dmz-bps-in (the name of the "item" and the "key"). How do you make a macro read that data? I've seen references to something like {HOST:ITEM.last(0)} but that doesn't work. I've tried things like {HOST:net-pan-fw-eth1-310-dmz-bps-in.last(0)} and that doesn't work.

So those are my two questions. How can a macro reference a different/specific host; and how can a macro reference/read a specific ITEM or KEY in that host?