/* 3D 棋盘（js/3d-board.js）：#bdBoard 加上 .bd3 时，2D SVG 藏起来、换成 3D 舞台；3D 失败就去掉 .bd3，2D 原样出现 */
.bd-board.bd3 { padding: 0; margin: 0 -10px; background: none; box-shadow: none; border-radius: 22px; }
.bd-board.bd3 > .bd-svg { display: none; }
.bd3-stage { position: relative; width: 100%; max-height: 68vh; border-radius: 22px; overflow: hidden; cursor: pointer; -webkit-tap-highlight-color: transparent;
  background: radial-gradient(90% 70% at 50% 40%, color-mix(in srgb, var(--bd-bg1) 70%, #000), var(--bd-bg2) 80%);
  box-shadow: inset 0 0 0 1px color-mix(in srgb, var(--bd-edge) 28%, transparent), 0 26px 50px -26px var(--bd-glow); }
.bd3-stage canvas { opacity: 0; transition: opacity .45s ease; }
.bd3-stage.on canvas { opacity: 1; }