Site Builder and Mobile Devices
Jamroom Developers
Yeah you can definitely do some of this in CSS since each widget has a unique ID.
I'm hesitant to add this directly to Site Builder though - it's just not something anyone else has needed. My worry is someone sets a widget to be "mobile only" and doesn't see it and it becomes a support issue. Site Builder is designed for those that aren't technical - more technical choices typically isn't a good idea.
But we'll definitely check it out. Thanks!