This is very neat but gamepad mapping can't be configured and the browser default "standard" mapping doesn't work very well (at least with my Xbox one controller).
If you visit chrome://flags you can enable "Restrict gamepad access" which will disable the default controller's mapping.
Click the wrench next to controller 1/2, click in each of the input boxes and press the button on the controller to map it. I had no issues setting up my XB1 controller.
Click the wrench next to controller 1/2, click in each of the input boxes and press the button on the controller to map it. I had no issues setting up my XB1 controller.