UI improvements
Checkers is played by two opponents on opposite sides of the game board. One player has the dark pieces (black); the other has the light pieces (white). Players alternate turns. A player can not move an opponent's pieces. A move consists of moving a piece diagonally to an adjacent unoccupied square. If the adjacent square contains an opponent's piece, and the square immediately beyond it is vacant, the piece may be captured (and removed from the game) by jumping over it.
Only the dark squares of the checkerboard are used. A piece can only move diagonally into an unoccupied square. The player without pieces remaining, or who cannot move due to being blocked, loses the game.
