Why doesn't the Google Chrome Extensions Tutorial tutorial work?

Question

Google Chrome

I decided to write a small extension for chrome, but the experience is zero. I started reading the Google tutorial, ended up here: Programmatic injection

From there, I followed the link to a training example: make_page_red

I downloaded the files, added an extension in the browser. The problem is that it doesn't work. The button appears, the inscription on it changes with the corresponding period, but when pressed, the page background remains the same.

I would be glad if someone can help me figure out why this simple example does not work.

Answer 1

1. judging by the manifest chrome 18+?
2. didn't add !important to the changed CSS?