CSS is not a thing to learn, it's the collection of some concepts you have to consider as a guide and follow blindly.
Why So Many People used to say, CSS is hard?
if you're not interested in CSS then don't list it in your skillset and portfolio. The Mastery of CSS is a huge thing and some of the beginners are listing that their CSS skills are 90% to 100% but they are talking about the Syntax, not CSS.
Another side is when a newbie of CSS, tries to design Websites but the mind is not generating the design and Inspiration(Oh My God!). it's good but limited. CSS for those people who want to create designs to inspire other people. All the syntax and Framework Guide in front of them. But they are still following the nav => header => sections => aside => footer traditional designs.
maybe they just learned how to put a border, but they didn't learn where to put it? so it comes with lots of websites surfing and observing the behavior. The syntax is not everything. if you are only the master of syntax, please don't list CSS in your skillset. it hurts All of us(Ui Designer).
If you are a programmer, then focus on programming, just learn syntax. but don't say that you can design websites.