I use sometime display-none for my mobile website.
Do you know how Google interprets the content “hidden”? Is it penalized? And what do you think about using the “display-none”?
If it’s just a mobile stylesheet applied to the regular page, and the normal non-mobile stylesheet has those elements displayed, then it won’t be a problem - Google can understand that sometimes content is hidden from mobiles, or is hidden from view and revealed by an action, and it won’t count that as shady practice.
Google understands that users do not want to see as much text on a mobile site as they do on a PC. They will view this practice as helping the end user, and will therefore not penalize you.
You will only get penalized for shady practices that do not help the end user in some way.