<div class="centered-circle"></div>

<script>
    ws = new WebSocket("ws://localhost/server")
    ws.onmessage = event => {
        if (event.data == "user_start_message") {
            document.body.style.backgroundColor = "white"
            document.querySelector('.centered-circle')
                .style.backgroundColor = "black"
        } else if (event.data == "user_end_message") {
            document.body.style.backgroundColor = "black"
            document.querySelector('.centered-circle')
                .style.backgroundColor = "white"
        }
    }
</script>