Start by don’t repeating yourself in CSS

CSS is a convenient programming language, we can be as lazy developer as we want and it will still work. I assume that you know what the results will be if you choose the lazy way. We share techniques and philosophy with software engineering principles, like DRY, Single Responsibility, Open/closed principle, Separations of concerns among others. DRY is a useful principle to get started with CSS if you aren’t yet.