[Tkinter] ttk-->treeview-->tag_configure() not work over Python3.6

[Larz60+]

I'm running 3.9.1 and this script functions as written on my system. (Linux mint 20)

You should download a copy of John Shipman's tkinter reference manual here
This version from 2013 is the latest, but tkinter has changed little since then.

If you want to dig deeper (really not necessary but interesting), there's a three volume illustrated set TCP/IP illistrated (Addison-Wesley Professional Computing Series) that can be bought used on Amazon fairly inexpensively