added decrement function and button

lib/main.dart

@@ -38,6 +38,12 @@ class _MyHomePageState extends State<MyHomePage> {
     });
   }
 
+  void _decrementCounter() {
+    setState(() {
+      _counter--;
+    });
+  }
+
   @override
   Widget build(BuildContext context) {
     return Scaffold(
@@ -59,11 +65,29 @@ class _MyHomePageState extends State<MyHomePage> {
           ],
         ),
       ),
-      floatingActionButton: FloatingActionButton(
+      floatingActionButton: Stack(
+        children: <Widget>[
+          Padding(
+            padding: EdgeInsets.only(left: 31),
+            child: Align(
+              alignment: Alignment.bottomLeft,
+              child: FloatingActionButton(
                 onPressed: _incrementCounter,
                 tooltip: 'Increment',
                 child: const Icon(Icons.add),
               ),
+            ),
+          ),
+          Align(
+            alignment: Alignment.bottomRight,
+            child: FloatingActionButton(
+              onPressed: _decrementCounter,
+              tooltip: 'Decrement',
+              child: const Icon(Icons.remove),
+            ),
+          ),
+        ],
+      ),
     );
   }
 }