Plug the SPIKE Prime hub in with USB, turn it on, then click Connect to hub. The page stops any program on the hub (Ctrl-C) and starts a tiny loop that streams the motor reading. Arrow keys also move the kid, for testing without a hub.
Keyboard: ← → (or A / D) move the kid · F full screen · S settings
Flipping only affects the game picture, not this settings box.
Browsers keep sound off until someone clicks or presses a key on the page once.