There currently is one option to travel by night train from Ústí nad Labem (Czech Republic) to Hamburg (Germany), taking approximately 7 hours: Namely the RJ 478. These lines are operated by České dráhy and Deutsche Bahn.
České dráhy (ČD) is the Czech national railway operator, running domestic and international passenger trains connecting the Czech Republic with neighboring countries.
Deutsche Bahn (DB) exited the actual night train business in 2016. However, it operates around a dozen Intercity and Eurocity trains that run exclusively at night.
These trains only have first and second class seats. The cars remain lit throughout the night and the seats cannot be reclined.