1. save file as json

2. modify html to show all data
3. set black as the background color of appbar

lib/main.dart

@@ -79,7 +79,8 @@ class _MyHomePageState extends State<MyHomePage> {
         // TRY THIS: Try changing the color here to a specific color (to
         // Colors.amber, perhaps?) and trigger a hot reload to see the AppBar
         // change color while the other colors stay the same.
-        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
+        backgroundColor:
+            Colors.black, //Theme.of(context).colorScheme.inversePrimary,
         // Here we take the value from the MyHomePage object that was created by
         // the App.build method, and use it to set our appbar title.
         title: Text(widget.title),
@@ -163,7 +164,7 @@ class _MyHomePageState extends State<MyHomePage> {
           await methodChannel.invokeMethod('getExternalDownloadsPath');
       DateTime now = DateTime.now();
       String formattedDate = DateFormat('yyyy-MM-dd_HH-mm-ss').format(now);
-      File file = File('$downloadsPath/$formattedDate.txt');
+      File file = File('$downloadsPath/$formattedDate.json');
       var sink = file.openWrite();
       sink.write(jsonEncode(mLightSensorEvents));
       await sink.flush();