Building chrome extension. Help understanding service workers.

Hi all,

Can anyone point me to any resources for how to implement service workers for chrome extensions using manifest 3.0 (or show me with the attached code)?

This is my first coding project and I'm trying to figure out how to inject one of two different CSS files (main.css or main2.css) based on the state (1/0) of a button in popup.html.

For reference, I'm a quick learner, but a beginner.

Here's a link to the GitHub with the code: https://github.com/Kasi21/ChromeBackground

Thanks in advance!

Kas