Hi Loic,
you might be able to override a "display: none;" style, but then websites that want to hide the link, can still just position it out of the visible area, remove it with _javascript_ after the site was loaded, or use the Shadow DOM to hide it. So if somebody wants to hide the web labels link, he can do it without that LibreJS will be able to know that it is hidden.
Beside the technical difficulties to prevent hiding the web labels link, I think there are legit cases, where we should allow websites to hide that link. For example on pages that doesn't contain any other navigation elements, like pages that show media in full screen.
So wouldn't it be better to allow websites to hide the link without any hacks, with a <link> tag in the header. And show the link, doesn't matter whether it is visible on the the web page, additionally in the LibreJS overlay?
Cheers
Sebastian