What is the theme in Olive's Ocean by Kevin Henkes?

In many cases, this is the typical coming of age story. Martha is an intelligent girl but death has not personally touched her life until the summer Olive dies. Even then, Martha is able to keep some distance because she and Olive are little more than acquaintances. But as Martha learns about Olive's life and her hopes and dreams, she comes to realize that the two girls have a great deal in common.