You can search the Love Book in Kugou and you may find what you are looking for

The Love Book’s Episode of Saving Feng Chen

Further question:

You'd better click on the link to listen

Answer:

Is it haunting - Wei Jia

Question:

Then How does the background music compare with the opening song? Besides, the opening song doesn’t sound good at all

Following question:

I don’t know if you have listened to 36:26 to 37:44 in the link. That piece of background music

Answer:

Listen to it

Supplement:

Just find it yourself from Kuwo Music. There are so many, I don’t know which one it is

Following question:

Do you think it is a deliberate background music (it has nothing to do with the opening and ending songs) or it is just pure music

Answer:

You ask me, how do I know?

Further question:

But this background music is paired with Han Shixuan and Zhan Shujuan’s Nursery rhymes are even better