There is the textbook "Computational Complexity: A Modern Approach" by Arora and Barak with a freely accessible draft: https://theory.cs.princeton.edu/complexi

There is the textbook "Computational Complexity: A Modern Approach" by Arora and Barak with a freely accessible draft: https://theory.cs.princeton.edu/complexity/book.pdf https://theory.cs.princeton.edu/complexity/book.pdf