I have definitely seen magazine CSS before, so it should work. That CSS in particular works as well when I use it as a userstyle in Stylus, so there's nothing wrong with the CSS.
So I'm guessing the issue here is precedence. Your browser is probably preferring a different style over your magazine CSS. You should be able to check in the dev tools (f12 in chromium browsers) whether that's the case, as your style should be listed there when selecting an element it applies to, and, if I'm correct, the background should be crossed out.