Most solitary confinement prison cells in the USA are smaller than a horse stall so there's not much room in a solitary confinement cell and they usually have no windows to the outside or any natural sunlight coming into the prison cell.
The average square feet of a solitary confinement prison cell measures 80 square feet and some bathrooms are larger than that.
There is usually a window on the door to the solitary confinement cell so that the guards can look into the cell to check on the inmate being housed in the solitary confinement cells.
The inmate is held in the prison cell in solitary confinement for 23 to 24 hours per day and some days they may not leave their prison cell.
Being in solitary confinement makes the prisoner more dangerous and it really solves nothing but sometimes a prisoner is already so dangerous that they need to be housed in the prison cell alone so that they do not harm other prisoners and guards.
Some prisoners in solitary confinement are allowed books and some are not allowed books or anything else but the essentials.
If you're in solitary confinement and have had all your privileges taken away from you then no you won't be allowed books in solitary confinement or anything else.
But if you still have your privileges then yes you can have books to read while in solitary confinement which is a good thing because even a book could help the prisoner from going even more insane.
I go insane at times just being stuck inside my house on cold winter days when the weather is very nasty outside and so I could not imagine being locked in a solitary confinement cell for 23 or 24 hours per day for months on end or even sometimes decades.
There have been some prisoners who lived in solitary confinement for 20 years and longer without being let out except for maybe 1 hour per day and into a rec cage.