Don't like the look of mismatched books but need to fill those built-ins?
Simply take a few old books you won't be reading and cover them with pretty wrapping paper!
Just make sure the paper is thick enough to hide anything underneath.
I also spray painted a book to add a different texture to the bunch.
The options are endless and easy to change if you get bored with the look!
To cover the books, I did a search on YouTube of how to cover text books
(remember doing that in math class with an old paper bag?)