/* Keep browser selection and long-press callouts out of the game surface. */
html, body, body * {
  -webkit-user-select: none;
  user-select: none;
  -webkit-touch-callout: none;
  -webkit-user-drag: none;
}
/* Held movement controls must not turn into scrolling or zoom gestures. */
canvas, [data-key] { touch-action: none; }
/* Menus and ordinary puzzle buttons still allow page scrolling. */
button, a { -webkit-tap-highlight-color: transparent; }