Overnight train travel to/from Guangzhou

Hi,
My visiting parents are interested in traveling from Guangzhou to Shanghai via an overnight train sleeper and would like to learn more about the experience.
I guess they would like to know what the sleeper accomodation is like (I imagine relatively basic) and whether there is catering available.
Would be grateful to hear from anyone who has done this or similar train travel in China.
Cheers!