Rapid Rules - How to play BoxOff

About BoxOff, from BoardGameGeek:

BoxOff is a solo abstract strategy game. It rises above the level of a mere puzzle because of its random set-up and user-defined board size. The random set-up makes it like a playing-card solitaire game. The game is played on a rectangular board of any size, as long as it has an even number of squares. 7x8, 8x12, and 12x15 are common sizes. The board is filled with stones or marbles in various colors. For an easy game, use 3 colors. For a game of medium difficulty, use 4 colors. For a difficult game use 5 colors. There must be an even number of each color, because they're going to be removed in pairs. Typically you would use an equal number of each color. A pair of stones of the same color may be removed from the board if the pair define opposite corners of a rectangle that contains no other stones. They could be in a line (a 1xn rectangle) or diagonal corners of a non-linear rectangle. The goal is to remove all the stones. This game was first described in Games Magazine in 2013, and later in the Abstract Games magazine in 2020. There have been electronic versions for iOS and Android. BoxOff is now being published by NewVenture Games in three versions: a board game, peg game, and travel-size.