The face liveness UI is developed by AWS, see it's official demo. KYC integrates it in an iframe, we can only customize a bit.
So I ran the official demo, deployed it on Amplify: https://main.d2m1suc7miy4d9.amplifyapp.com/. KYC hosts it via an iframe.
Note: on the desktop, there is only one camera. on the mobile, only the front camera can be used.