I want to change the way youtube look for me. just change simple things in the css , like when you inspect the page.

I played a little with python and selenium to scrape a webpage but it opens a new window when I run the code.
so I was wondering if there is a way to use it with an already open tabs and rerun the code when I refresh the page
Or there is some other ways ? it doesn’t have to be with python or selenium.

thanks in advance