feat(fallback): use dynamic filename

template/assets/style.css

@@ -13,13 +13,39 @@ body {
     background-position: center;
     background-repeat: no-repeat;
     background-size: cover;
-    background-image: url("../operator/operator_bg.png");
     height: 100%;
     width: 100%;
     touch-action: none;
     -ms-touch-action: none;
 }
 
+#dev {
+    position: fixed;
+    left: 0;
+    top: 0;
+    background-color: white;
+}
+
+#widget-wrapper, #container, #fallback {
+    width: 100%; 
+    height: 100%;
+}
+
+.hide {
+    display: none;
+}
+
+#fallback.show {
+    display: flex;
+    align-items: center;
+    margin: auto;
+    background-position: center;
+    background-repeat: no-repeat;
+    background-size: cover;
+    width: 100%;
+    height: 100%;
+}
+
 .logo {
     position: fixed;
     left: 0;
@@ -32,21 +58,6 @@ body {
     opacity: 0.3;
 }
 
-.widget-wrapper {
-    display: flex;
-    align-items: center;
-}
-
-.fallback {
-    margin: auto;
-    background-position: center;
-    background-repeat: no-repeat;
-    background-size: cover;
-    background-image: url("../operator/fallback.png");
-    width: 100%;
-    height: 100%;
-}
-
 .website-settings {
     position: fixed;
     left: 0;