.diff-btn {
  opacity: 0.55;
  font-size: 13px;
  padding: 6px 16px;
}
.diff-btn.active {
  opacity: 1;
  background: linear-gradient(135deg, var(--accent), var(--accent-soft));
  color: #fff;
  box-shadow: 0 2px 8px rgba(237,194,46,0.4);
  transform: scale(1.06);
}

#game-canvas {
  display: block;
  width: 100%;
  max-width: 360px;
  /* scale down proportionally so canvas never overflows the viewport */
  height: auto;
  max-height: calc(100dvh - 168px);
  margin: 0 auto;
  cursor: pointer;
  touch-action: none;
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-lg);
}

.board-wrapper {
  display: flex;
  justify-content: center;
}