No matter where you end up in tech, you can't go wrong with learning more CSS. Even if you're gravitating towards back end, project management, user experience, etc, being better at CSS will make you better at whatever you're doing.
Recently, an amazing resource came out — Josh Comeau's CSS for JavaScript Developers.
It's expensive ($399), but happily, DPI has negotiated a discount and purchased multiple licenses. Send a message to an instructor when you're ready to go through it, and include your personal email address (not your student worker address) in the message, and we'll send you an invitation to the course.
It's called CSS for JavaScript Developers, but it's really for everyone, not just JavaScript developers. You can skip the chapters that deal with integrating CSS into JavaScript.