It is a good way to use up some of those left over sheets of paper too.
But remember that any additions to the card will prevent it from closing when the book is laid down so keep them as flat as you can.
You will find many ideas for small gifts that will be especially welcome for Christmas and Birthdays, or even special occasions like
Mothers Day,
and this is another one to add to your repetoire.
They are always a much more personal touch to any card that you give and I am sure that the recipient would be delighted with, treasure, and appreciate the time you have taken to make some thing just for them.