Вот тут очень удобная штука для чтения минимизированного css. Магия.
Enter your messy, minified, or obfuscated CSS Style Sheets into the field above to have it cleaned up and made pretty. The editor above also contains helpful line numbers and syntax highlighting. There are many option to tailor the beautifier to your personal formatting tastes.
When do you use
Often when writing CSS Style Sheets your indentation, spacing, and other formatting can become a bit disorganized. It is also common for multiple developers to work on a single project who have different formatting techniques. This tool is helpful for making the formatting of a file consistent. It is also common for CSS Style Sheets to be minified or obfuscated. You can use this tool to make that code look pretty and readable so it is easier to edit.
А это, напротив, для минимизации https://csscompressor.com.
Понятное дело, с использованием сборщиков, этот сервис теряет свою актуальность, но на всякий случай пусть будет в копилке знаний. А вот первый самое то, в свете современных технологий (мне пару раз пригодился даже).