<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>