Do browsers parse `CSS` on `CSS` file loading? Or parsing is done once the whole `CSS` file is downloaded by a browser? Is there a difference in different browser's approch on it? Where can I find this kind of low level information?

This question is not a duplicate of [Load and execution sequence of a web page?](https://stackoverflow.com/questions/1795438/load-and-execution-sequence-of-a-web-page) question, as it relates only to CSS download / parsing part, whereas in the related question there is no answer with detailed discription of synchronious / asynchronious `CSS` file download / parsing.