When I started learning HTML and CSS I relied on frameworks like Foundation and Bootstrap to do the heavy lifting of any project I was working on. Early on I learned Sass so I could customize what components I was including in my final CSS. I started out using pretty much everything included in the frameworks. I slowly started removing components until all that was left were some helper classes and the grid system. Eventually, I dropped frameworks like these altogether.
Currently, depending on the size of the project, Iâ€™ll either use my own grid system or use something like Susy. In every project I also use Normalize and Bourbon. So, at most Iâ€™m including three third-party libraries in my CSS (Normalize is the only one that outputs actual CSS...Bourbon only supplies mixins and functions, as does Susy). The rest of my CSS is all handwritten Sass.
I see this as a natural progression in learning a new language or technology. Start with a lot of assistance, see how much more experienced professionals do this type of work, how they structure and write CSS or HTML, and learn from them. Once you become more comfortable, reduce your need for their code.
I put this to the test recently on that podcast player I was talking about. In the initial prototype I had both jQuery and a third-party audio library to do the majority of the work. As I began running into issues with the audio library (and having little success finding any decent alternatives), I kept finding myself in the source code mangling it to suit my needs. At one point I just gave up and decided to write my own small audio library. With a little help from our friends at Mozilla, writing a tailor-made audio player was insanely simple.