It's going to take you a bit of time as it's a course, and a little bit of money but really not a lot.
Code School is the best e-learning site I've came across. It's nice, simple, funny, and the teachers are really good. https://www.codeschool.com/courses/css-cross-country
If you plan to do business with Webflow and want to improve CSS, this is a very good starting point.