openvidu-livekit-tutorials/openvidu-library-react/src/App.css

#join{
    text-align: center;
}

#join, #session {
    position: absolute;
    margin: auto;
    top: 100px;
    bottom: 0;
    left: 0;
    right: 0;
    height: 70%;
    width: 70%;
}