I know that i can extract elements using css selectors with libs such as bs4. but I have a problem where I don't know names of css classes used to style elements I need to extract, but I know that all this elements have common rule applied to them("position:fixed;" in my case). Is there any convenient way(some library) that I can use to do this?
Selenium is a very good python library for automation, but it allows for web scraping and selecting multiple using their CSS selectors and more. This should allow you to store all the elements with the

("position:fixed;" in my case)

Using selenium you would be able to extract the data, then you could manipulate the data however you would want. There are many ways to parse the data itself, so please be more specific on that part.
If in doubt send the website link as a comment and ill check the CSS selectors for you.
Hope this has solved the issue.
Is there any convenient way to parse html elements by ccs styles applied to them in python?