Styles must be improved (full width for smartphones, selectable text for PGN...)
Tooltip text should fade (even when mouse stay on it, especially for small screens)
Checkered stage 2: switch button at reserve position (or on top).
-If a played disconnect right after opponent sent a move, it might be never received: secure this
Mode expert: game.js, button on top (with online indicator)
Turn indicator on top too (black or white)
+incheck by checkered pawns: not marked (because of turn changed?)