Created the bottom control bar

src/cipher_disk/lib/floating_toolbar.dart

@@ -1,4 +1,5 @@
 import 'package:flutter/material.dart';
+import 'package:flutter/services.dart';
 
 class FloatingToolbar extends StatelessWidget {
   const FloatingToolbar({super.key, required this.primColor});
@@ -6,28 +7,50 @@ class FloatingToolbar extends StatelessWidget {
 
   @override
   Widget build(BuildContext context) {
+    Color textColor = primColor.computeLuminance() > 0.5
+        ? Colors.black
+        : Colors.white;
+
     return BottomAppBar(
       color: primColor,
 
+      child: IconTheme(
+        data: IconThemeData(color: textColor),
         child: Row(
-        mainAxisAlignment: MainAxisAlignment.center,
           children: [
-          Text(
-            'Key:',
-            style: TextStyle(
-              fontSize: 24,
-              color: primColor.computeLuminance() > 0.5
-                  ? Colors.black
-                  : Colors.white,
+            Text('Key:', style: TextStyle(fontSize: 20, color: textColor)),
+            Padding(padding: EdgeInsetsGeometry.all(5)),
+            SizedBox(
+              width: 30,
+              child: TextField(
+                keyboardType: TextInputType.number,
+                decoration: InputDecoration(
+                  border: UnderlineInputBorder(),
+                  hintText: '12',
+                  hintStyle: TextStyle(color: Colors.yellow),
+                ),
+                style: TextStyle(color: textColor, fontSize: 20),
+                inputFormatters: [FilteringTextInputFormatter.digitsOnly],
               ),
             ),
             IconButton(
-            icon: Icon(Icons.code, size: 50),
-            color: Colors.green,
+              tooltip: 'Increase key by +1',
+              icon: const Icon(Icons.plus_one),
+              onPressed: () {},
+            ),
+            IconButton(
+              tooltip: 'Decrease key by -1',
+              icon: const Icon(Icons.exposure_minus_1_outlined),
+              onPressed: () {},
+            ),
+            IconButton(
+              tooltip: 'Swap',
+              icon: const Icon(Icons.swap_horiz),
               onPressed: () {},
             ),
           ],
         ),
+      ),
     );
   }
 }

src/cipher_disk/lib/main.dart

@@ -61,7 +61,7 @@ class _MyHomePageState extends State<MyHomePage> {
         ),
       ),
 
-      floatingActionButton: FloatingToolbar(primColor: primColor),
+      bottomNavigationBar: FloatingToolbar(primColor: primColor),
     );
   }
 }