CSS is the basic skill of front-end engineers, but many people who are obsessed with learning JavaScript are not solid. Some people may have hurried through the W3school website, just a few superficial understandings of the common concept of CSS, jumping out of a deep hole in JavaScript. In fact, the more complex logic in JavaScript is likely to solve the problem with CSS in a few lines of style, and performance is fine.
The reason why CSS can become an elegant language and a corresponding refactoring engineer is because the language itself has a very strong value, and it's not easy to really understand it. Starting with the CSS Zen garden, writing CSS becomes an art. From CSS2.1 to 3 to 4,css covered by the content and achievable features have been greatly enriched, so that the learning cost of CSS is more and more high. A lot of knowledge, a knowledge point to learn, can always learn to understand.
CSS Learning Catalog