Segregate script canvas context

src/main/resources/templates/broadcast.html

@@ -13,7 +13,7 @@
     </head>
     <body class="broadcast-body">
         <canvas id="broadcast-canvas"></canvas>
-        <canvas id="broadcast-script-canvas"></canvas>
+        <div id="broadcast-script-layer" class="broadcast-script-layer"></div>
         <script th:inline="javascript">
             const broadcaster = /*[[${broadcaster}]]*/ "";
         </script>