Mounted to the wall with either brass or stainless.
Then the chrome elbow makes up the difference between the tank and the bowl. Normally these were set on a 14" rough-in.
Except that yours connects from the top of the bowl so matching that up may need some sort of shimming at the wall to make it work. Have you dry set the bowl on the flange to see what you will be working with?
I would make sure there is backing in the wall for that.
Nobody roughs at 14" anymore though. Standard rough is at 12" from the wall. What do you have for a rough-in measurement?
This is what I normally see in older homes.
And how a tank gets mounted.