Add some text, start with styling, and add minimalistic event handler

resources/public/style.css

@@ -4,11 +4,50 @@
     box-sizing: border-box
 }
 
+html,
 body {
-    color: #222
+    min-height: 100vh;
+    padding: 0;
+    margin: 0
+}
+
+body {
+    color: #222;
+    line-height: 1.2
+}
+
+#welcome-message {
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
+    width: 640px;
+    max-width: 100%;
+    padding: 48px;
+
+    z-index: 20;
+    opacity: 1;
+    transition: opacity .2s ease;
+}
+
+#welcome-message.hidden {
+    pointer-events: none;
+    opacity: 0;
+}
+
+.container {
+    position: absolute;
+    top: 50%;
+    left: 50%;
+    transform: translate(-50%, -50%);
+    width: 640px;
+    max-width: 100%;
+    padding: 48px;
+    text-align: center;
 }
 
 canvas#result {
+    /* needs position: absolute so it's rendered above the video */
     position: absolute;
     z-index: 10;
 }