How to add and save custom js, css to a page in a browser?

Question

css

You need to add your css and js to the page / tab in the browser and so that it would work after reloading the page, of course, so that all this would be saved only in my browser)

What are the ways? or some good browser extensions

Answer 1

Add-ons Tampermonkey Greasemonkey and others like
you can include both css and javascript

Answer 2

https://developer.chrome.com/extensions/content_scripts

Answer 3

https://github.com/openstyles/stylus - there are plugins for chrome, ff, etc.