  We report on recent theory progress in understanding the production of heavy
quarkonium in heavy-ion collisions based on the in-medium heavy-quark potential
extracted from lattice QCD simulations. On the one hand, the proper in-medium
potential allows us to study the spectral properties of heavy quarkonium in
thermal equilibrium, from which we estimate the $\psi^\prime$ to $J/\psi$ ratio
in heavy-ion collisions. On the other hand, the potential provides a central
ingredient in the description of the real-time evolution of heavy-quarkonium
formulated in the open-quantum-systems framework.
