Appearance
This is remembered on this device and nowhere else. A tablet on a stand and a laptop at home can be set differently while being the same account.
The page
A score is ink on paper however dark the room is. What changes at night is how much light the paper is throwing at you — so this turns the lamp down rather than turning the score inside out.
The app itself
Whenever this device can reach the server, the app asks whether there is a newer version and fetches it in the background. A page opened after that is the new one. The button is for when that has not happened and something is stuck: it throws away every cached copy and fetches the app again from the server.