Add an "Are you sure?" dialog for the “New Game” function
It should not be possible for the user to lost his game by hitting a bad shortcut (Ctrl-N) or by misclicking an entry in the hamburger menu. There should be a security for the “New Game” function.
The correct solution is probably to go like 2048: a “New Game” menubutton at the left of the headerbar that allows choosing next game size, and Ctrl-N that allows opening this menu (with optionally a Ctrl-Shift-N for directly restarting). But that forces to remove the current “Restart icon” button (the one that replace the “solve icon” one), as that would feel too much.
Edited by Andre Klapper