Take a look at the Stylish extension, which has hundreds of styles for various websites that users created for it:

https://userstyles.org/

Using such pre-created styles is a lot faster, easier, and more convenient than manually customizing each and every element by hand yourself.

Knowing how to do that is, of course, a good skill to have when you actually do want to do something custom for which a pre-rolled style does not exist or when existing styles do something you don't like.