I'm not CSS expert, but I've spent a good amount of time hacking CSS for my own pet projects, and believe me: A little bit goes a long way, but there's plenty you can learn if you want to go deep.

The design site CSS-Tricks has their own guide for learning HTML and CSS—but they’ve compiled plenty of alternatives into a wide-ranging but approachable list.

The Web Development Master Class Certification Bundle contains 35 hours of educational content that will teach you how to code in HTML, CSS, JavaScript, Bootstrap, PHP, MySQL, and more.