How to replace the contents of a div block through Chrome Extensions?

Question

Google Chrome

I will never figure it out. It is required in the background script background.js to check each request. If the request corresponds to the site site.ru, then we look for the div block of the class_name class and replace its content with another value.
Maybe somewhere already there is a ready-made implementation. I know that the task is simple, but I can't figure it out.

Answer 1

Can anyone help?