PostCSS has been my personal favorite out of all the tools for writing CSS for the past year and a half. Setup is really easy, it features tons of extremely useful plugins and it has great performance. One of my favorite plugins is definitely possess-preset-env.
Every developer asks himself at some point, which should I use? IDs or Classes? We'll answer this question by approaching the CSS Specificity concept, what is it and how is it related to these CSS Selectors.