With CSS unintended consequences are always problems of scoping things better. If I give semantically meaningful CSS classes to my semantic HTML and scope my rules to apply to their intended place in the pages, then unintended consequences don't happen. If I roll like: "Oh, I want this list to look differently, lets make a global scope ul/ol style!" then I am asking for trouble later on. When I write a CSS rule, I should always be thinking about the scope and whether my rules are truly something universally applicable to that scope.