Othello black and white stone graphics:
Shudan Goban by SabakiHQ (MIT)
https://github.com/SabakiHQ/Shudan
Original assets: css/stone_1.svg, css/stone_-1.svg
Used without modifications, as stone-black.svg and stone-white.svg.
License: /licenses/Shudan-MIT.txt
Game controls and the 8x8 layout remain Kotsumori's integration code.