Error in warning "Class not imported" when class file is required_once

A class "Book.php" in the same folder as "inheritence.php. The Book.php is required in the inheritence.php" yet i get a warning that "Class 'Book' is not imported." Why?

<img width="838" height="290" alt="Image" src="https://github.com/user-attachments/assets/bb0cb756-5a8f-4518-9e50-7451f92974c9" />