I had been using similar projects such as skeleton[0] and milligram[1] for small experiments such as repfl[2], and wanted to create something similar that I would find aesthetically pleasing and that would fit in as little space as possible. The current version of concrete.css is less than 1kb minzipped!
[0] http://getskeleton.com/
[1] https://milligram.io/
[2] https://repfl.ch/