hide map overlay until map is loaded

htdocs/css/map.css

@@ -25,12 +25,19 @@ ul {
     padding-inline-start: 25px;
 }
 
+/* don't show the filter in it's initial position */
 .openwebrx-map-legend {
+    display: none;
     background-color: #fff;
     padding: 10px;
     margin: 10px;
 }
 
+/* show it as soon as google maps has moved it to its container */
+.openwebrx-map .openwebrx-map-legend {
+    display: block;
+}
+
 .openwebrx-map-legend ul {
     list-style-type: none;
     padding: 0;