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.