It’s been more than 3 decades and we’re still using CSS for styling websites. Even though the way we write CSS has changed a little bit in recent years following the rise of JavaScript frameworks. CSS architecture has been moving to direction of local styled components than global shared stylesheet.
CSS is simple to learn and here to stay for many years to come. As frontend developer, you are expected to be solid at CSS styling no matter what technologies you’re using.
This page covers some topics beyond the basics that might bring your CSS skill to the next level. There is no clear hierarchy here, you can read articles in the order you want.