fix: loan book success confirm form

lib/src/providers/auth_provider.dart

@@ -42,6 +42,10 @@ class AuthProvider with ChangeNotifier {
     notifyListeners();
   }
 
+  void setLoanBookSuccess(bool value) {
+    loanBookSuccess = value;
+  }
+
   Future<void> signIn(
       BuildContext context, String username, String password) async {
     try {

lib/src/widgets/forms/book_loan_form.dart

@@ -25,17 +25,24 @@ class _LoanBookForm extends State<LoanBookForm> {
   Widget build(BuildContext context) {
     return Consumer<AuthProvider>(builder: (context, authProvider, child) {
       if (authProvider.loanBookSuccess) {
-        return AlertDialog(
+        final screenSize = MediaQuery.of(context).size;
+        return Center(
+          child: SizedBox(
+            height: screenSize.height * 0.4,
+            child: AlertDialog(
               title: const Text(
                 'Loan book succed!',
                 style: TextStyle(fontSize: 20.0),
               ),
               content: FilledButton(
                 onPressed: () {
+                  authProvider.setLoanBookSuccess(false);
                   Navigator.of(context).pop();
                 },
                 child: const Text('Continue'),
               ),
+            ),
+          ),
         );
       }
       return Container(