The basic idea is to absolutely position an element far, far away from the visible screen so that it isn't visible, but screen readers can still announce it. There's a lot more to learn about accessibility. I recommend that you start by checking out the article at https://css-tricks.com/places-its-tempting-to-use-display-none-but-dont/ for more information, at least on how to use off-screen hidden techniques, and then go from there with regard to accessibility:
Web accessibility is a topic with so much depth that it deserves a book of its own. So I cannot do it thorough justice ...
