CSS Variables have been in Firefox for a year and a half now, and I’ve been using them in my own projects for at least a year, while I’m producing the thing in the first place—then when I have it as I like it, if it’s not purely for me, I rewrite it for inferior browsers (though I believe I could use something like PostCSS instead; I just haven’t).<p>They really are a <i>marvellous</i> thing; my favourite example would be the construction of truly responsive interfaces, tweaked for optimality at many levels and continuous, rather than just things with three or four breakpoints; with preprocessors, it’s tedious and painful; with CSS variables it’s <i>easy</i> and <i>obvious</i>—it pushes you in a direction that is <i>so much easier to make</i>.<p>In essence, they are solving a substantially different set of problems, but one that is more useful and more general; the sorts of things people did with preprocessor variables can normally be done in better ways with CSS Variables; it helps guide you to a better position.