Wait until they realize that on mobile they can use accelerometer data to keep the element in the same position in space across translations of the device.
Wait, I have to hold my phone how in order to see the div? ಠ_ಠ
Stop giving them ideas! :(
So the content falls down at 10 m/s^2 unless you're falling alongside it.
position: hyperfixed;
Translations? Not far enough, got to include rotations: https://developer.mozilla.org/en-US/docs/Web/API/Device_orie...
(And yes, CSS can rotate around all three axes, so you could make a div that resists rotating your device in addition to resisting translation...)