A neat way to go is to work with a library, I've been trying out material-ui.com on a project and really like it, then I just override with inline CSS anytime I need to, which, frankly, is infrequently. Each component only requires the styles it needs so it retains modularity and does a lot of work for you. getessence.io is also a nice one, with a bit more of a learning curve, I thought.