What's a good tutorial for learning CSS?

While you don't need to know HTML & CSS to use Buttondown, if you really want to get creative with the look and feel of your newsletter it helps to be familiar with the lingua franca of the internet itself.

Our favorite tutorial on the subject is the free tutorial offered by Khan Academy: it's approachable, easy, and will arm you with knowledge for a wide variety of platforms (not just Buttondown!)