I like to go with a clean slate with just a CSS reset stylesheet added to the project.
However, if you're working with SASS you should take a look at bourbon.io which is a great mixins library.
And most people like to start with a grid system, here's a nice discussion on Sass based grid systems (hashnode.com/post/what-are-the-best-sass-based-grid-systems-cij1tj1h200a0lv5347vco54g).
hope it helps! 😊