-End of game a bit too verbose: should just say "Black win" ... + show PGN
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.
+If a played disconnect right after opponent sent a move, it might be never received: secure this
+Think about non-conventional variants with 2 kings for example: undercheck highlight?
+ --> underCheck should return a vector in this case. Adapt.