diff --git a/assets/AppAsset.php b/assets/AppAsset.php
index f0ab4dd8b..56e81dac0 100644
--- a/assets/AppAsset.php
+++ b/assets/AppAsset.php
@@ -6,9 +6,14 @@
  * @license https://www.yiiframework.com/license/
  */
 
+declare(strict_types=1);
+
 namespace app\assets;
 
+use yii\bootstrap5\BootstrapAsset;
 use yii\web\AssetBundle;
+use yii\web\View;
+use yii\web\YiiAsset;
 
 /**
  * Main application asset bundle.
@@ -27,10 +32,10 @@ class AppAsset extends AssetBundle
         'js/color-mode.js',
     ];
     public $jsOptions = [
-        'position' => \yii\web\View::POS_HEAD,
+        'position' => View::POS_HEAD,
     ];
     public $depends = [
-        'yii\web\YiiAsset',
-        'yii\bootstrap5\BootstrapAsset'
+        YiiAsset::class,
+        BootstrapAsset::class,
     ];
 }
diff --git a/commands/HelloController.php b/commands/HelloController.php
index 28dba79cd..7da32fb0d 100644
--- a/commands/HelloController.php
+++ b/commands/HelloController.php
@@ -6,6 +6,8 @@
  * @license https://www.yiiframework.com/license/
  */
 
+declare(strict_types=1);
+
 namespace app\commands;
 
 use yii\console\Controller;
@@ -26,9 +28,9 @@ class HelloController extends Controller
      * @param string $message the message to be echoed.
      * @return int Exit code
      */
-    public function actionIndex($message = 'hello world')
+    public function actionIndex(string $message = 'hello world'): int
     {
-        echo $message . "\n";
+        echo "{$message}\n";
 
         return ExitCode::OK;
     }
diff --git a/config/console.php b/config/console.php
index ca429affa..4f8283823 100644
--- a/config/console.php
+++ b/config/console.php
@@ -15,12 +15,12 @@
     ],
     'components' => [
         'cache' => [
-            'class' => 'yii\caching\FileCache',
+            'class' => \yii\caching\FileCache::class,
         ],
         'log' => [
             'targets' => [
                 [
-                    'class' => 'yii\log\FileTarget',
+                    'class' => \yii\log\FileTarget::class,
                     'levels' => ['error', 'warning'],
                 ],
             ],
@@ -41,13 +41,13 @@
     // configuration adjustments for 'dev' environment
     $config['bootstrap'][] = 'gii';
     $config['modules']['gii'] = [
-        'class' => 'yii\gii\Module',
+        'class' => \yii\gii\Module::class,
     ];
     // configuration adjustments for 'dev' environment
     // requires version `2.1.21` of yii2-debug module
     $config['bootstrap'][] = 'debug';
     $config['modules']['debug'] = [
-        'class' => 'yii\debug\Module',
+        'class' => \yii\debug\Module::class,
         // uncomment the following to add your IP if you are not connecting from localhost.
         //'allowedIPs' => ['127.0.0.1', '::1'],
     ];
diff --git a/config/db.php b/config/db.php
index bc75e616f..d83cbf1c9 100644
--- a/config/db.php
+++ b/config/db.php
@@ -1,7 +1,7 @@
 <?php
 
 return [
-    'class' => 'yii\db\Connection',
+    'class' => \yii\db\Connection::class,
     'dsn' => 'mysql:host=localhost;dbname=yii2basic',
     'username' => 'root',
     'password' => '',
diff --git a/config/test.php b/config/test.php
index fb5e2929e..6320bcdf0 100644
--- a/config/test.php
+++ b/config/test.php
@@ -9,6 +9,9 @@
 return [
     'id' => 'basic-tests',
     'basePath' => dirname(__DIR__),
+    'bootstrap' => [
+        \app\tests\Support\MailerBootstrap::class,
+    ],
     'aliases' => [
         '@bower' => '@vendor/bower-asset',
         '@npm'   => '@vendor/npm-asset',
@@ -18,10 +21,9 @@
         'db' => $db,
         'mailer' => [
             'class' => \yii\symfonymailer\Mailer::class,
-            'viewPath' => '@app/mail',
-            // send all mails to a file by default.
+            'messageClass' => \yii\symfonymailer\Message::class,
             'useFileTransport' => true,
-            'messageClass' => 'yii\symfonymailer\Message'
+            'viewPath' => '@app/mail',
         ],
         'assetManager' => [
             'basePath' => __DIR__ . '/../web/assets',
@@ -30,7 +32,7 @@
             'showScriptName' => true,
         ],
         'user' => [
-            'identityClass' => 'app\models\User',
+            'identityClass' => \app\models\User::class,
         ],
         'request' => [
             'cookieValidationKey' => 'test',
diff --git a/config/web.php b/config/web.php
index 8b9dd3f94..8c43a34e2 100644
--- a/config/web.php
+++ b/config/web.php
@@ -7,6 +7,16 @@
     'id' => 'basic',
     'basePath' => dirname(__DIR__),
     'bootstrap' => ['log'],
+    'container' => [
+        'singletons' => [
+            \yii\mail\MailerInterface::class => [
+                'class' => \yii\symfonymailer\Mailer::class,
+                // send all mails to a file by default.
+                'useFileTransport' => true,
+                'viewPath' => '@app/mail',
+            ],
+        ],
+    ],
     'aliases' => [
         '@bower' => '@vendor/bower-asset',
         '@npm'   => '@vendor/npm-asset',
@@ -17,26 +27,21 @@
             'cookieValidationKey' => '',
         ],
         'cache' => [
-            'class' => 'yii\caching\FileCache',
+            'class' => \yii\caching\FileCache::class,
         ],
         'user' => [
-            'identityClass' => 'app\models\User',
+            'identityClass' => \app\models\User::class,
             'enableAutoLogin' => true,
         ],
         'errorHandler' => [
             'errorAction' => 'site/error',
         ],
-        'mailer' => [
-            'class' => \yii\symfonymailer\Mailer::class,
-            'viewPath' => '@app/mail',
-            // send all mails to a file by default.
-            'useFileTransport' => true,
-        ],
+        'mailer' => \yii\mail\MailerInterface::class,
         'log' => [
             'traceLevel' => YII_DEBUG ? 3 : 0,
             'targets' => [
                 [
-                    'class' => 'yii\log\FileTarget',
+                    'class' => \yii\log\FileTarget::class,
                     'levels' => ['error', 'warning'],
                 ],
             ],
@@ -58,14 +63,14 @@
     // configuration adjustments for 'dev' environment
     $config['bootstrap'][] = 'debug';
     $config['modules']['debug'] = [
-        'class' => 'yii\debug\Module',
+        'class' => \yii\debug\Module::class,
         // uncomment the following to add your IP if you are not connecting from localhost.
         //'allowedIPs' => ['127.0.0.1', '::1'],
     ];
 
     $config['bootstrap'][] = 'gii';
     $config['modules']['gii'] = [
-        'class' => 'yii\gii\Module',
+        'class' => \yii\gii\Module::class,
         // uncomment the following to add your IP if you are not connecting from localhost.
         //'allowedIPs' => ['127.0.0.1', '::1'],
     ];
diff --git a/controllers/SiteController.php b/controllers/SiteController.php
index a60bffafb..93a7da2f7 100644
--- a/controllers/SiteController.php
+++ b/controllers/SiteController.php
@@ -1,21 +1,37 @@
 <?php
 
+declare(strict_types=1);
+
 namespace app\controllers;
 
 use Yii;
+use app\models\ContactForm;
+use app\models\LoginForm;
+use yii\captcha\CaptchaAction;
 use yii\filters\AccessControl;
+use yii\filters\VerbFilter;
+use yii\base\Security;
+use yii\mail\MailerInterface;
 use yii\web\Controller;
+use yii\web\ErrorAction;
 use yii\web\Response;
-use yii\filters\VerbFilter;
-use app\models\LoginForm;
-use app\models\ContactForm;
 
 class SiteController extends Controller
 {
+    public function __construct(
+        $id,
+        $module,
+        private readonly MailerInterface $mailer,
+        private readonly Security $security,
+        $config = [],
+    ) {
+        parent::__construct($id, $module, $config);
+    }
+
     /**
      * {@inheritdoc}
      */
-    public function behaviors()
+    public function behaviors(): array
     {
         return [
             'access' => [
@@ -41,14 +57,14 @@ public function behaviors()
     /**
      * {@inheritdoc}
      */
-    public function actions()
+    public function actions(): array
     {
         return [
             'error' => [
-                'class' => 'yii\web\ErrorAction',
+                'class' => ErrorAction::class,
             ],
             'captcha' => [
-                'class' => 'yii\captcha\CaptchaAction',
+                'class' => CaptchaAction::class,
                 'fixedVerifyCode' => YII_ENV_TEST ? 'testme' : null,
                 'transparent' => true,
             ],
@@ -60,7 +76,7 @@ public function actions()
      *
      * @return string
      */
-    public function actionIndex()
+    public function actionIndex(): string
     {
         return $this->render('index');
     }
@@ -70,21 +86,21 @@ public function actionIndex()
      *
      * @return Response|string
      */
-    public function actionLogin()
+    public function actionLogin(): Response|string
     {
         if (!Yii::$app->user->isGuest) {
             return $this->goHome();
         }
 
-        $model = new LoginForm();
-        if ($model->load(Yii::$app->request->post()) && $model->login()) {
+        $model = new LoginForm($this->security);
+
+        if ($model->load($this->request->post()) && $model->login()) {
             return $this->goBack();
         }
 
         $model->password = '';
-        return $this->render('login', [
-            'model' => $model,
-        ]);
+
+        return $this->render('login', ['model' => $model]);
     }
 
     /**
@@ -92,7 +108,7 @@ public function actionLogin()
      *
      * @return Response
      */
-    public function actionLogout()
+    public function actionLogout(): Response
     {
         Yii::$app->user->logout();
 
@@ -104,17 +120,24 @@ public function actionLogout()
      *
      * @return Response|string
      */
-    public function actionContact()
+    public function actionContact(): Response|string
     {
         $model = new ContactForm();
-        if ($model->load(Yii::$app->request->post()) && $model->contact(Yii::$app->params['adminEmail'])) {
+
+        $contact = $model->load($this->request->post()) && $model->contact(
+            $this->mailer,
+            Yii::$app->params['adminEmail'],
+            Yii::$app->params['senderEmail'],
+            Yii::$app->params['senderName'],
+        );
+
+        if ($contact) {
             Yii::$app->session->setFlash('contactFormSubmitted');
 
             return $this->refresh();
         }
-        return $this->render('contact', [
-            'model' => $model,
-        ]);
+
+        return $this->render('contact', ['model' => $model]);
     }
 
     /**
@@ -122,7 +145,7 @@ public function actionContact()
      *
      * @return string
      */
-    public function actionAbout()
+    public function actionAbout(): string
     {
         return $this->render('about');
     }
diff --git a/docs/images/about-dark.png b/docs/images/about-dark.png
index 6da920794..7e3fd1ac3 100644
Binary files a/docs/images/about-dark.png and b/docs/images/about-dark.png differ
diff --git a/docs/images/about-light.png b/docs/images/about-light.png
index 3d7ba7076..da9cf3988 100644
Binary files a/docs/images/about-light.png and b/docs/images/about-light.png differ
diff --git a/docs/images/contact-success-dark.png b/docs/images/contact-success-dark.png
new file mode 100644
index 000000000..b602be278
Binary files /dev/null and b/docs/images/contact-success-dark.png differ
diff --git a/docs/images/contact-success-light.png b/docs/images/contact-success-light.png
new file mode 100644
index 000000000..86c47314b
Binary files /dev/null and b/docs/images/contact-success-light.png differ
diff --git a/docs/images/error-dark.png b/docs/images/error-dark.png
new file mode 100644
index 000000000..406189126
Binary files /dev/null and b/docs/images/error-dark.png differ
diff --git a/docs/images/error-light.png b/docs/images/error-light.png
new file mode 100644
index 000000000..7d47520bd
Binary files /dev/null and b/docs/images/error-light.png differ
diff --git a/models/ContactForm.php b/models/ContactForm.php
index f001d2192..fafdf189b 100644
--- a/models/ContactForm.php
+++ b/models/ContactForm.php
@@ -1,26 +1,27 @@
 <?php
 
+declare(strict_types=1);
+
 namespace app\models;
 
-use Yii;
 use yii\base\Model;
+use yii\mail\MailerInterface;
 
 /**
  * ContactForm is the model behind the contact form.
  */
 class ContactForm extends Model
 {
-    public $name;
-    public $email;
-    public $subject;
-    public $body;
-    public $verifyCode;
-
+    public string $name = '';
+    public string $email = '';
+    public string $subject = '';
+    public string $body = '';
+    public string $verifyCode = '';
 
     /**
      * @return array the validation rules.
      */
-    public function rules()
+    public function rules(): array
     {
         return [
             // name, email, subject and body are required
@@ -35,7 +36,7 @@ public function rules()
     /**
      * @return array customized attribute labels
      */
-    public function attributeLabels()
+    public function attributeLabels(): array
     {
         return [
             'verifyCode' => 'Verification Code',
@@ -44,15 +45,20 @@ public function attributeLabels()
 
     /**
      * Sends an email to the specified email address using the information collected by this model.
-     * @param string $email the target email address
-     * @return bool whether the model passes validation
+     *
+     * @param MailerInterface $mailer the mailer component.
+     * @param string $email the target email address.
+     * @param string $senderEmail the sender email address.
+     * @param string $senderName the sender name.
+     *
+     * @return bool whether the model passes validation.
      */
-    public function contact($email)
+    public function contact(MailerInterface $mailer, string $email, string $senderEmail, string $senderName): bool
     {
         if ($this->validate()) {
-            Yii::$app->mailer->compose()
+            $mailer->compose()
                 ->setTo($email)
-                ->setFrom([Yii::$app->params['senderEmail'] => Yii::$app->params['senderName']])
+                ->setFrom([$senderEmail => $senderName])
                 ->setReplyTo([$this->email => $this->name])
                 ->setSubject($this->subject)
                 ->setTextBody($this->body)
@@ -60,6 +66,7 @@ public function contact($email)
 
             return true;
         }
+
         return false;
     }
 }
diff --git a/models/LoginForm.php b/models/LoginForm.php
index 5304eecf4..c39c6ff93 100644
--- a/models/LoginForm.php
+++ b/models/LoginForm.php
@@ -1,29 +1,36 @@
 <?php
 
+declare(strict_types=1);
+
 namespace app\models;
 
 use Yii;
 use yii\base\Model;
+use yii\base\Security;
 
 /**
  * LoginForm is the model behind the login form.
  *
  * @property-read User|null $user
- *
  */
 class LoginForm extends Model
 {
-    public $username;
-    public $password;
-    public $rememberMe = true;
+    public string $username = '';
+    public string $password = '';
+    public bool $rememberMe = true;
 
-    private $_user = false;
+    private User|null $_user = null;
+    private bool $_userLoaded = false;
 
+    public function __construct(private readonly Security $security, $config = [])
+    {
+        parent::__construct($config);
+    }
 
     /**
      * @return array the validation rules.
      */
-    public function rules()
+    public function rules(): array
     {
         return [
             // username and password are both required
@@ -42,12 +49,12 @@ public function rules()
      * @param string $attribute the attribute currently being validated
      * @param array $params the additional name-value pairs given in the rule
      */
-    public function validatePassword($attribute, $params)
+    public function validatePassword(string $attribute, array|null $params): void
     {
         if (!$this->hasErrors()) {
             $user = $this->getUser();
 
-            if (!$user || !$user->validatePassword($this->password)) {
+            if (!$user || !$this->security->validatePassword($this->password, $user->passwordHash)) {
                 $this->addError($attribute, 'Incorrect username or password.');
             }
         }
@@ -57,11 +64,12 @@ public function validatePassword($attribute, $params)
      * Logs in a user using the provided username and password.
      * @return bool whether the user is logged in successfully
      */
-    public function login()
+    public function login(): bool
     {
         if ($this->validate()) {
             return Yii::$app->user->login($this->getUser(), $this->rememberMe ? 3600 * 24 * 30 : 0);
         }
+
         return false;
     }
 
@@ -70,10 +78,11 @@ public function login()
      *
      * @return User|null
      */
-    public function getUser()
+    public function getUser(): User|null
     {
-        if ($this->_user === false) {
+        if (!$this->_userLoaded) {
             $this->_user = User::findByUsername($this->username);
+            $this->_userLoaded = true;
         }
 
         return $this->_user;
diff --git a/models/User.php b/models/User.php
index 6343a98b3..304575ae1 100644
--- a/models/User.php
+++ b/models/User.php
@@ -1,37 +1,43 @@
 <?php
 
+declare(strict_types=1);
+
 namespace app\models;
 
-class User extends \yii\base\BaseObject implements \yii\web\IdentityInterface
+use yii\base\BaseObject;
+use yii\web\IdentityInterface;
+
+class User extends BaseObject implements IdentityInterface
 {
-    public $id;
-    public $username;
-    public $password;
-    public $authKey;
-    public $accessToken;
+    public int|string $id = '';
+    public string $username = '';
+    public string $passwordHash = '';
+    public string $authKey = '';
+    public string $accessToken = '';
 
-    private static $_users = [
+    private static array $_users = [
         '100' => [
             'id' => '100',
             'username' => 'admin',
-            'password' => 'admin',
+            // password: admin
+            'passwordHash' => '$2y$13$gYAywKSkhfZDq9FLNdm7buKnvlRxDexf5xipSMAxQPDUxpaptmZJu',
             'authKey' => 'test100key',
             'accessToken' => '100-token',
         ],
         '101' => [
             'id' => '101',
             'username' => 'demo',
-            'password' => 'demo',
+            // password: demo
+            'passwordHash' => '$2y$13$alRLq1PGVMlGYwS/Y3iy3ewQns1Z8ol8Iq6Zb5k7ZwEhblA1aL29y',
             'authKey' => 'test101key',
             'accessToken' => '101-token',
         ],
     ];
 
-
     /**
      * {@inheritdoc}
      */
-    public static function findIdentity($id)
+    public static function findIdentity($id): static|null
     {
         return isset(self::$_users[$id]) ? new static(self::$_users[$id]) : null;
     }
@@ -39,7 +45,7 @@ public static function findIdentity($id)
     /**
      * {@inheritdoc}
      */
-    public static function findIdentityByAccessToken($token, $type = null)
+    public static function findIdentityByAccessToken($token, $type = null): static|null
     {
         foreach (self::$_users as $user) {
             if ($user['accessToken'] === $token) {
@@ -56,7 +62,7 @@ public static function findIdentityByAccessToken($token, $type = null)
      * @param string $username
      * @return static|null
      */
-    public static function findByUsername($username)
+    public static function findByUsername(string $username): static|null
     {
         foreach (self::$_users as $user) {
             if (strcasecmp($user['username'], $username) === 0) {
@@ -70,7 +76,7 @@ public static function findByUsername($username)
     /**
      * {@inheritdoc}
      */
-    public function getId()
+    public function getId(): int|string
     {
         return $this->id;
     }
@@ -78,7 +84,7 @@ public function getId()
     /**
      * {@inheritdoc}
      */
-    public function getAuthKey()
+    public function getAuthKey(): string|null
     {
         return $this->authKey;
     }
@@ -86,19 +92,8 @@ public function getAuthKey()
     /**
      * {@inheritdoc}
      */
-    public function validateAuthKey($authKey)
+    public function validateAuthKey($authKey): bool
     {
         return $this->authKey === $authKey;
     }
-
-    /**
-     * Validates password
-     *
-     * @param string $password password to validate
-     * @return bool if password provided is valid for current user
-     */
-    public function validatePassword($password)
-    {
-        return $this->password === $password;
-    }
 }
diff --git a/tests/Support/MailerBootstrap.php b/tests/Support/MailerBootstrap.php
new file mode 100644
index 000000000..898c1aa53
--- /dev/null
+++ b/tests/Support/MailerBootstrap.php
@@ -0,0 +1,28 @@
+<?php
+
+declare(strict_types=1);
+
+namespace app\tests\Support;
+
+use Yii;
+use yii\base\Application;
+use yii\base\BootstrapInterface;
+use yii\mail\MailerInterface;
+
+/**
+ * Registers the application mailer component as the DI container singleton for {@see MailerInterface}.
+ *
+ * Codeception replaces `components.mailer` with its own TestMailer to capture sent emails.
+ * Since the DI container is configured before the mailer mock, this bootstrap ensures
+ * the DI singleton resolves to the same mailer instance used by the application.
+ */
+final class MailerBootstrap implements BootstrapInterface
+{
+    /**
+     * @param Application $app Application instance.
+     */
+    public function bootstrap($app): void
+    {
+        Yii::$container->setSingleton(MailerInterface::class, $app->mailer);
+    }
+}
diff --git a/tests/Unit/LoginTest.php b/tests/Unit/LoginTest.php
index efc19afc4..05e52aa62 100644
--- a/tests/Unit/LoginTest.php
+++ b/tests/Unit/LoginTest.php
@@ -7,18 +7,19 @@
 use app\controllers\SiteController;
 use app\models\User;
 use Yii;
-use yii\console\Application;
+use yii\base\Security;
 use yii\web\View;
 
-use function dirname;
-
 final class LoginTest extends \Codeception\Test\Unit
 {
     public function testRenderLoginWrongUsername(): void
     {
-        $controller = new SiteController('site', Yii::$app);
-
-        Yii::$app->controller = $controller;
+        $controller = new SiteController(
+            'site',
+            Yii::$app,
+            Yii::$app->mailer,
+            new Security(),
+        );
 
         $view = new View(['context' => $controller]);
 
@@ -27,9 +28,9 @@ public function testRenderLoginWrongUsername(): void
         $controller->actionLogin();
 
         self::assertStringNotContainsString(
-            '<button type="submit" class="nav-link btn btn-link logout text-decoration-none">Logout (admin)</button>',
+            'Logout (admin)',
             $view->render('//layouts/main.php', ['content' => 'Hello World°']),
-            'Failed asserting that the logout link is rendered for a logged-in user.',
+            'Failed asserting that the logout link is not rendered for a wrong username.',
         );
     }
 }
diff --git a/tests/Unit/LogoutTest.php b/tests/Unit/LogoutTest.php
index aa62c17d0..f6e38af2c 100644
--- a/tests/Unit/LogoutTest.php
+++ b/tests/Unit/LogoutTest.php
@@ -7,6 +7,7 @@
 use app\controllers\SiteController;
 use app\models\User;
 use Yii;
+use yii\base\Security;
 use yii\web\IdentityInterface;
 use yii\web\View;
 
@@ -16,9 +17,12 @@ public function testRenderLogoutLinkWhenUserIsLoggedIn(): void
     {
         $user = User::findIdentity('100');
 
-        $controller = new SiteController('site', Yii::$app);
-
-        Yii::$app->controller = $controller;
+        $controller = new SiteController(
+            'site',
+            Yii::$app,
+            Yii::$app->mailer,
+            new Security(),
+        );
 
         $view = new View(['context' => $controller]);
 
@@ -34,18 +38,27 @@ public function testRenderLogoutLinkWhenUserIsLoggedIn(): void
 
         Yii::$app->user->login($user);
 
+        $html = $view->render('//layouts/main.php', ['content' => 'Hello World°']);
+
         self::assertStringContainsString(
-            '<button type="submit" class="nav-link btn btn-link logout text-decoration-none">Logout (admin)</button>',
-            $view->render('//layouts/main.php', ['content' => 'Hello World°']),
+            'Logout (admin)',
+            $html,
             'Failed asserting that the logout link is rendered for a logged-in user.',
         );
+        self::assertStringContainsString(
+            'data-method="post"',
+            $html,
+            'Failed asserting that the logout link uses POST method.',
+        );
 
         $controller->actionLogout();
 
+        $html = $view->render('//layouts/main.php', ['content' => 'Hello World°']);
+
         self::assertStringNotContainsString(
-            '<button type="submit" class="nav-link btn btn-link logout text-decoration-none">Logout (admin)</button>',
-            $view->render('//layouts/main.php', ['content' => 'Hello World°']),
-            'Failed asserting that the logout link is rendered for a logged-in user.',
+            'Logout (admin)',
+            $html,
+            'Failed asserting that the logout link is not rendered after logout.',
         );
     }
 }
diff --git a/tests/Unit/Models/ContactFormTest.php b/tests/Unit/Models/ContactFormTest.php
index 98bf8f7e7..405e48750 100644
--- a/tests/Unit/Models/ContactFormTest.php
+++ b/tests/Unit/Models/ContactFormTest.php
@@ -5,6 +5,7 @@
 namespace app\tests\Unit\Models;
 
 use app\models\ContactForm;
+use Yii;
 use yii\mail\MessageInterface;
 
 final class ContactFormTest extends \Codeception\Test\Unit
@@ -23,7 +24,7 @@ public function testEmailIsSentOnContact()
             'verifyCode' => 'testme',
         ];
 
-        verify($model->contact('admin@example.com'))->notEmpty();
+        verify($model->contact(Yii::$app->mailer, 'admin@example.com', 'noreply@example.com', 'Example.com mailer'))->notEmpty();
 
         // using Yii2 module actions to check email was sent
         $this->tester->seeEmailIsSent();
diff --git a/tests/Unit/Models/LoginFormTest.php b/tests/Unit/Models/LoginFormTest.php
index acff2f1a4..3aea667ce 100644
--- a/tests/Unit/Models/LoginFormTest.php
+++ b/tests/Unit/Models/LoginFormTest.php
@@ -6,6 +6,7 @@
 
 use app\models\LoginForm;
 use Yii;
+use yii\base\Security;
 
 final class LoginFormTest extends \Codeception\Test\Unit
 {
@@ -19,6 +20,7 @@ protected function _after()
     public function testLoginNoUser()
     {
         $this->_model = new LoginForm(
+            new Security(),
             [
                 'username' => 'not_existing_username',
                 'password' => 'not_existing_password',
@@ -32,6 +34,7 @@ public function testLoginNoUser()
     public function testLoginWrongPassword()
     {
         $this->_model = new LoginForm(
+            new Security(),
             [
                 'username' => 'demo',
                 'password' => 'wrong_password',
@@ -46,6 +49,7 @@ public function testLoginWrongPassword()
     public function testLoginCorrect()
     {
         $this->_model = new LoginForm(
+            new Security(),
             [
                 'username' => 'demo',
                 'password' => 'demo',
diff --git a/tests/Unit/Models/UserTest.php b/tests/Unit/Models/UserTest.php
index b390675a2..ac2f34950 100644
--- a/tests/Unit/Models/UserTest.php
+++ b/tests/Unit/Models/UserTest.php
@@ -47,7 +47,5 @@ public function testValidateUser()
 
         verify($user->validateAuthKey('test100key'))->notEmpty();
         verify($user->validateAuthKey('test102key'))->empty();
-        verify($user->validatePassword('admin'))->notEmpty();
-        verify($user->validatePassword('123456'))->empty();
     }
 }
diff --git a/tests/_bootstrap.php b/tests/_bootstrap.php
index 7ceaeaad0..6d9316c43 100644
--- a/tests/_bootstrap.php
+++ b/tests/_bootstrap.php
@@ -1,7 +1,9 @@
 <?php
 
-defined('YII_DEBUG',);
-define('YII_ENV', 'test');
+declare(strict_types=1);
+
+defined('YII_DEBUG') or define('YII_DEBUG', true);
+defined('YII_ENV') or define('YII_ENV', 'test');
 
 require_once __DIR__ . '/../vendor/yiisoft/yii2/Yii.php';
 require __DIR__ . '/../vendor/autoload.php';
diff --git a/views/layouts/_footer.php b/views/layouts/_footer.php
new file mode 100644
index 000000000..53c6920a8
--- /dev/null
+++ b/views/layouts/_footer.php
@@ -0,0 +1,41 @@
+<?php
+
+declare(strict_types=1);
+
+/** @var yii\web\View $this */
+
+use yii\helpers\Html;
+
+?>
+<footer id="footer" class="mt-auto py-3 bg-body-tertiary">
+    <div class="container">
+        <div class="row text-body-secondary">
+            <div class="col-md-6 text-center text-md-start">&copy; My Company <?= date('Y') ?></div>
+            <div class="col-md-6 text-center text-md-end">
+                <a href="https://www.yiiframework.com/" rel="external" class="text-body-secondary text-decoration-none">
+                    <?= Yii::t(
+                        'yii',
+                        'Powered by {yii}',
+                        ['yii' => ''],
+                    ) ?>
+                    <?= Html::img(
+                        '@web/images/yii_logo_light.svg',
+                        [
+                            'alt' => 'Yii Framework',
+                            'class' => 'align-text-bottom footer-logo-light',
+                            'height' => '28',
+                        ],
+                    ) ?>
+                    <?= Html::img(
+                        '@web/images/yii_logo_dark.svg',
+                        [
+                            'alt' => 'Yii Framework',
+                            'class' => 'align-text-bottom footer-logo-dark',
+                            'height' => '28',
+                        ],
+                    ) ?>
+                </a>
+            </div>
+        </div>
+    </div>
+</footer>
diff --git a/views/layouts/_head.php b/views/layouts/_head.php
new file mode 100644
index 000000000..c440ca89b
--- /dev/null
+++ b/views/layouts/_head.php
@@ -0,0 +1,40 @@
+<?php
+
+declare(strict_types=1);
+
+/** @var yii\web\View $this */
+
+use app\assets\AppAsset;
+
+AppAsset::register($this);
+
+$this->registerCsrfMetaTags();
+$this->registerMetaTag(
+    ['charset' => Yii::$app->charset],
+    'charset',
+);
+$this->registerMetaTag(
+    [
+        'name' => 'viewport',
+        'content' => 'width=device-width, initial-scale=1',
+    ],
+);
+$this->registerMetaTag(
+    [
+        'name' => 'description',
+        'content' => $this->params['meta_description'] ?? ''
+    ],
+);
+$this->registerMetaTag(
+    [
+        'name' => 'keywords',
+        'content' => $this->params['meta_keywords'] ?? ''
+    ],
+);
+$this->registerLinkTag(
+    [
+        'rel' => 'icon',
+        'type' => 'image/x-icon',
+        'href' => Yii::getAlias('@web/favicon.ico'),
+    ],
+);
diff --git a/views/layouts/_header.php b/views/layouts/_header.php
new file mode 100644
index 000000000..e16b2a51a
--- /dev/null
+++ b/views/layouts/_header.php
@@ -0,0 +1,65 @@
+<?php
+
+declare(strict_types=1);
+
+/** @var yii\web\View $this */
+
+use yii\bootstrap5\Nav;
+use yii\bootstrap5\NavBar;
+use yii\helpers\Html;
+
+$items = [
+    [
+        'label' => 'Home',
+        'url' => ['/site/index'],
+    ],
+    [
+        'label' => 'About',
+        'url' => ['/site/about'],
+    ],
+    [
+        'label' => 'Contact',
+        'url' => ['/site/contact'],
+    ],
+    [
+        'label' => 'Login',
+        'url' => ['/site/login'],
+        'visible' => Yii::$app->user->isGuest,
+    ],
+    [
+        'label' => 'Logout (' . Html::encode(Yii::$app->user->identity?->username ?? '') . ')',
+        'url' => ['/site/logout'],
+        'linkOptions' => [
+            'data-method' => 'post',
+            'class' => 'logout',
+        ],
+        'visible' => !Yii::$app->user->isGuest,
+    ],
+];
+
+?>
+<header id="header">
+    <?php NavBar::begin(
+        [
+            'brandLabel' => Yii::$app->name,
+            'brandUrl' => Yii::$app->homeUrl,
+            'options' => ['class' => 'navbar-expand-md navbar-dark bg-dark fixed-top']
+        ],
+    ) ?>
+    <?= Nav::widget(
+        [
+            'options' => ['class' => 'navbar-nav me-auto'],
+            'encodeLabels' => false,
+            'items' => $items,
+        ],
+    ) ?>
+    <?= Html::button(
+        '&#127769;',
+        [
+            'id' => 'theme-toggle',
+            'class' => 'btn btn-link nav-link fs-5',
+            'aria-label' => 'Switch to dark mode',
+        ],
+    ) ?>
+    <?php NavBar::end() ?>
+</header>
diff --git a/views/layouts/main.php b/views/layouts/main.php
index 885b36639..02ccdf309 100644
--- a/views/layouts/main.php
+++ b/views/layouts/main.php
@@ -1,23 +1,15 @@
 <?php
 
+declare(strict_types=1);
+
 /** @var yii\web\View $this */
 /** @var string $content */
 
-use app\assets\AppAsset;
 use app\widgets\Alert;
 use yii\bootstrap5\Breadcrumbs;
-use yii\bootstrap5\Nav;
-use yii\bootstrap5\NavBar;
 use yii\helpers\Html;
 
-AppAsset::register($this);
-
-$this->registerCsrfMetaTags();
-$this->registerMetaTag(['charset' => Yii::$app->charset], 'charset');
-$this->registerMetaTag(['name' => 'viewport', 'content' => 'width=device-width, initial-scale=1']);
-$this->registerMetaTag(['name' => 'description', 'content' => $this->params['meta_description'] ?? '']);
-$this->registerMetaTag(['name' => 'keywords', 'content' => $this->params['meta_keywords'] ?? '']);
-$this->registerLinkTag(['rel' => 'icon', 'type' => 'image/x-icon', 'href' => Yii::getAlias('@web/favicon.ico')]);
+$this->render('_head');
 ?>
 <?php $this->beginPage() ?>
 <!DOCTYPE html>
@@ -29,39 +21,7 @@
 <body class="d-flex flex-column h-100">
 <?php $this->beginBody() ?>
 
-<header id="header">
-    <?php
-    NavBar::begin([
-        'brandLabel' => Yii::$app->name,
-        'brandUrl' => Yii::$app->homeUrl,
-        'options' => ['class' => 'navbar-expand-md navbar-dark bg-dark fixed-top']
-    ]);
-    echo Nav::widget([
-        'options' => ['class' => 'navbar-nav me-auto'],
-        'items' => [
-            ['label' => 'Home', 'url' => ['/site/index']],
-            ['label' => 'About', 'url' => ['/site/about']],
-            ['label' => 'Contact', 'url' => ['/site/contact']],
-            Yii::$app->user->isGuest
-                ? ['label' => 'Login', 'url' => ['/site/login']]
-                : '<li class="nav-item">'
-                    . Html::beginForm(['/site/logout'])
-                    . Html::submitButton(
-                        'Logout (' . Yii::$app->user->identity->username . ')',
-                        ['class' => 'nav-link btn btn-link logout text-decoration-none']
-                    )
-                    . Html::endForm()
-                    . '</li>'
-        ]
-    ]);
-    echo Html::button('&#127769;', [
-        'id' => 'theme-toggle',
-        'class' => 'btn btn-link nav-link fs-5',
-        'aria-label' => 'Switch to dark mode',
-    ]);
-    NavBar::end();
-    ?>
-</header>
+<?= $this->render('_header') ?>
 
 <main id="main" class="flex-grow-1" role="main">
     <div class="container">
@@ -73,20 +33,7 @@
     </div>
 </main>
 
-<footer id="footer" class="mt-auto py-3 bg-body-tertiary">
-    <div class="container">
-        <div class="row text-body-secondary">
-            <div class="col-md-6 text-center text-md-start">&copy; My Company <?= date('Y') ?></div>
-            <div class="col-md-6 text-center text-md-end">
-                <a href="https://www.yiiframework.com/" rel="external" class="text-body-secondary text-decoration-none">
-                    <?= Yii::t('yii', 'Powered by {yii}', ['yii' => '']) ?>
-                    <?= Html::img('@web/images/yii_logo_light.svg', ['alt' => 'Yii Framework', 'height' => '28', 'class' => 'align-text-bottom footer-logo-light']) ?>
-                    <?= Html::img('@web/images/yii_logo_dark.svg', ['alt' => 'Yii Framework', 'height' => '28', 'class' => 'align-text-bottom footer-logo-dark']) ?>
-                </a>
-            </div>
-        </div>
-    </div>
-</footer>
+<?= $this->render('_footer') ?>
 
 <?php $this->endBody() ?>
 </body>
diff --git a/views/site/about.php b/views/site/about.php
index 9a3ecc6f9..89c67e73c 100644
--- a/views/site/about.php
+++ b/views/site/about.php
@@ -7,14 +7,21 @@
 $this->title = 'About';
 $this->params['breadcrumbs'][] = $this->title;
 ?>
-<div class="site-about">
-    <h1><?= Html::encode($this->title) ?></h1>
+<div class="site-about d-flex align-items-center justify-content-center text-center">
+    <div class="site-about-content mx-auto">
+        <h1 class="display-6 fw-semibold mb-3">This is the About page.</h1>
 
-    <p>
-        This is the About page. You may modify the following file to customize its content:
-    </p>
+        <p class="text-body-secondary mb-4">
+            You may modify the following file to customize its content:
+            <?php if (YII_DEBUG): ?>
+                <code class="d-block mt-2"><?= __FILE__ ?></code>
+            <?php endif; ?>
+        </p>
 
-    <div class="alert alert-info d-flex align-items-center">
-        <code><?= __FILE__ ?></code>
+        <?= Html::a(
+            'Go to Homepage',
+            Yii::$app->homeUrl,
+            ['class' => 'btn btn-outline-primary btn-lg'],
+        ) ?>
     </div>
 </div>
diff --git a/views/site/contact.php b/views/site/contact.php
index f71f73faa..af1e7e0a5 100644
--- a/views/site/contact.php
+++ b/views/site/contact.php
@@ -15,27 +15,36 @@
 <div class="form-floating flex-grow-1">{input}{label}</div>{error}{hint}
 HTML;
 ?>
-<div class="site-contact py-5">
-    <h1 class="text-center"><?= Html::encode($this->title) ?></h1>
+<?php if (Yii::$app->session->hasFlash('contactFormSubmitted')): ?>
 
-    <?php if (Yii::$app->session->hasFlash('contactFormSubmitted')): ?>
+<div class="site-contact-success d-flex align-items-center justify-content-center text-center">
+    <div class="site-contact-success-content mx-auto">
+        <h1 class="display-6 fw-semibold mb-3">Message sent</h1>
 
-        <div class="alert alert-success">
+        <p class="text-body-secondary mb-4">
             Thank you for contacting us. We will respond to you as soon as possible.
-        </div>
-
-        <p>
-            Note that if you turn on the Yii debugger, you should be able
-            to view the mail message on the mail panel of the debugger.
-            <?php if (Yii::$app->mailer->useFileTransport): ?>
-                Because the application is in development mode, the email is not sent but saved as
-                a file under <code><?= Yii::getAlias(Yii::$app->mailer->fileTransportPath) ?></code>.
-                Please configure the <code>useFileTransport</code> property of the <code>mail</code>
-                application component to be false to enable email sending.
-            <?php endif; ?>
         </p>
 
-    <?php else: ?>
+        <?php if (YII_DEBUG && Yii::$app->mailer->useFileTransport): ?>
+            <p class="text-body-tertiary small mb-4">
+                Development mode: email saved under
+                <code><?= Yii::getAlias(Yii::$app->mailer->fileTransportPath) ?></code>
+            </p>
+        <?php endif; ?>
+
+        <?= Html::a(
+            'Send another message',
+            ['contact'],
+            ['class' => 'btn btn-outline-primary btn-lg'],
+        ) ?>
+    </div>
+</div>
+
+<?php else: ?>
+
+<div class="site-contact py-5">
+
+        <h1 class="text-center"><?= Html::encode($this->title) ?></h1>
 
         <div class="row justify-content-center">
             <div class="col-md-7 col-lg-6">
@@ -50,27 +59,40 @@
                     <?php $form = ActiveForm::begin(['id' => 'contact-form']); ?>
 
                     <?= $form->field($model, 'name', [
+                        'inputOptions' => [
+                            'class' => 'form-control',
+                            'placeholder' => 'Name',
+                            'autofocus' => true,
+                        ],
                         'options' => ['class' => 'input-group has-validation mb-3'],
                         'template' => sprintf($htmlIcon, '&#128100;'),
-                        'inputOptions' => ['class' => 'form-control', 'placeholder' => 'Name', 'autofocus' => true],
-                    ])->textInput() ?>
+                    ]) ?>
 
                     <?= $form->field($model, 'email', [
+                        'inputOptions' => [
+                            'class' => 'form-control',
+                            'placeholder' => 'Email',
+                        ],
                         'options' => ['class' => 'input-group has-validation mb-3'],
                         'template' => sprintf($htmlIcon, '&#9993;'),
-                        'inputOptions' => ['class' => 'form-control', 'placeholder' => 'Email'],
                     ]) ?>
 
                     <?= $form->field($model, 'subject', [
+                        'inputOptions' => [
+                            'class' => 'form-control',
+                            'placeholder' => 'Subject',
+                        ],
                         'options' => ['class' => 'input-group has-validation mb-3'],
                         'template' => sprintf($htmlIcon, '&#128172;'),
-                        'inputOptions' => ['class' => 'form-control', 'placeholder' => 'Subject'],
                     ]) ?>
 
                     <?= $form->field($model, 'body', [
+                        'inputOptions' => [
+                            'class' => 'form-control',
+                            'placeholder' => 'Body',
+                        ],
                         'options' => ['class' => 'form-floating mb-4'],
                         'template' => '{input}{label}{error}{hint}',
-                        'inputOptions' => ['class' => 'form-control', 'placeholder' => 'Body'],
                     ])->textarea() ?>
 
                     <div class="d-flex align-items-center gap-3 flex-wrap">
@@ -81,7 +103,13 @@
                             'template' => '<div class="d-flex align-items-center gap-2">{image}{input}</div>',
                         ]) ?>
 
-                        <?= Html::submitButton('Submit', ['class' => 'btn btn-primary px-4 ms-auto', 'name' => 'contact-button']) ?>
+                        <?= Html::submitButton(
+                            'Submit',
+                            [
+                                'class' => 'btn btn-primary px-4 ms-auto',
+                                'name' => 'contact-button',
+                            ],
+                        ) ?>
                     </div>
 
                     <?php ActiveForm::end(); ?>
@@ -89,6 +117,6 @@
                 </div>
             </div>
         </div>
-
-    <?php endif; ?>
 </div>
+
+<?php endif; ?>
diff --git a/views/site/error.php b/views/site/error.php
index a122733bd..1547fda6b 100644
--- a/views/site/error.php
+++ b/views/site/error.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 /** @var yii\web\View $this */
 /** @var string $name */
 /** @var string $message */
@@ -8,22 +10,23 @@
 use yii\helpers\Html;
 
 $this->title = $name;
+$statusCode = $exception->statusCode ?? 500;
 ?>
-<div class="site-error">
-
-    <h1><?= Html::encode($this->title) ?></h1>
-
-    <div class="alert alert-danger" role="alert">
-        <?= nl2br(Html::encode($message)) ?>
+<div class="site-error d-flex align-items-center justify-content-center text-center">
+    <div class="site-error-content mx-auto">
+        <h1 class="display-1 fw-bold text-body-secondary mb-0"><?= Html::encode($statusCode) ?></h1>
+
+        <h2 class="display-6 fw-semibold mb-3"><?= Html::encode($message) ?></h2>
+
+        <p class="text-body-secondary mb-4">
+            The above error occurred while the Web server was processing your request.
+            Please contact us if you think this is a server error. Thank you.
+        </p>
+
+        <?= Html::a(
+            'Go to Homepage',
+            Yii::$app->homeUrl,
+            ['class' => 'btn btn-outline-primary btn-lg'],
+        ) ?>
     </div>
-
-    <p class="text-body-secondary">
-        The above error occurred while the Web server was processing your request.
-    </p>
-    <p class="text-body-secondary">
-        Please contact us if you think this is a server error. Thank you.
-    </p>
-
-    <?= Html::a('Go to Homepage', Yii::$app->homeUrl, ['class' => 'btn btn-outline-primary']) ?>
-
 </div>
diff --git a/views/site/index.php b/views/site/index.php
index e3397d411..432cc4ae9 100644
--- a/views/site/index.php
+++ b/views/site/index.php
@@ -6,7 +6,7 @@
 
 $this->title = 'My Yii Application';
 ?>
-<div class="site-index d-flex flex-column justify-content-center h-100">
+<div class="site-index d-flex flex-column justify-content-center">
 
     <div class="p-5 mb-5 text-center bg-body-tertiary rounded-3">
         <h1 class="display-4 fw-bold">Congratulations!</h1>
@@ -14,7 +14,11 @@
         <p class="lead col-lg-8 mx-auto">You have successfully created your Yii-powered application.</p>
 
         <div class="d-grid gap-2 d-sm-flex justify-content-sm-center">
-            <?= Html::a('Get started with Yii', 'https://www.yiiframework.com', ['class' => 'btn btn-lg btn-success']) ?>
+            <?= Html::a(
+                'Get started with Yii',
+                'https://www.yiiframework.com',
+                ['class' => 'btn btn-lg btn-success'],
+            ) ?>
         </div>
     </div>
 
@@ -26,16 +30,44 @@
                     <div class="card-body">
                         <h2 class="h5"><?= Yii::t('app', 'Definitive Guide') ?></h2>
 
-                        <p><?= Yii::t('app', 'Learn Yii step by step: MVC structure, ActiveRecord, migrations, form validation, authentication, RBAC, REST APIs, caching, and testing. Everything you need is covered in one place, from basics to advanced topics.') ?></p>
+                        <p><?= Yii::t(
+                            'app',
+                            'Learn Yii step by step: MVC structure, ActiveRecord, migrations, form validation, authentication, RBAC, REST APIs, caching, and testing. Everything you need is covered in one place, from basics to advanced topics.',
+                        ) ?></p>
 
                         <ul class="list-unstyled small">
-                            <li><?= Html::a(Yii::t('app', 'Definitive Guide'), 'https://www.yiiframework.com/doc/guide/2.0/en', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a(Yii::t('app', 'API Reference'), 'https://www.yiiframework.com/doc/api/2.0', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a(Yii::t('app', 'Getting Started'), 'https://www.yiiframework.com/doc/guide/2.0/en/start-installation', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
+                            <li><?= Html::a(
+                                Yii::t('app', 'Definitive Guide'),
+                                'https://www.yiiframework.com/doc/guide/2.0/en',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                Yii::t('app', 'API Reference'),
+                                'https://www.yiiframework.com/doc/api/2.0',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                Yii::t('app', 'Getting Started'),
+                                'https://www.yiiframework.com/doc/guide/2.0/en/start-installation',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
                         </ul>
                     </div>
                     <div class="card-footer bg-transparent border-0">
-                        <?= Html::a('Yii Documentation &raquo;', 'https://www.yiiframework.com/doc/', ['class' => 'btn btn-outline-secondary']) ?>
+                        <?= Html::a(
+                            'Yii Documentation &raquo;',
+                            'https://www.yiiframework.com/doc/',
+                            ['class' => 'btn btn-outline-secondary'],
+                        ) ?>
                     </div>
                 </div>
             </div>
@@ -44,16 +76,44 @@
                     <div class="card-body">
                         <h2 class="h5"><?= Yii::t('app', 'Community Forum') ?></h2>
 
-                        <p><?= Yii::t('app', 'The Yii Forum is where thousands of developers share solutions, discuss best practices, and help each other. Before opening a GitHub issue, chances are someone already solved your problem there.') ?></p>
+                        <p><?= Yii::t(
+                            'app',
+                            'The Yii Forum is where thousands of developers share solutions, discuss best practices, and help each other. Before opening a GitHub issue, chances are someone already solved your problem there.',
+                        ) ?></p>
 
                         <ul class="list-unstyled small">
-                            <li><?= Html::a(Yii::t('app', 'Forum'), 'https://forum.yiiframework.com/', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a(Yii::t('app', 'GitHub'), 'https://github.com/yiisoft/yii2', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a(Yii::t('app', 'Telegram'), 'https://t.me/yii_framework_in_english', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
+                            <li><?= Html::a(
+                                Yii::t('app', 'Forum'),
+                                'https://forum.yiiframework.com/',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                Yii::t('app', 'GitHub'),
+                                'https://github.com/yiisoft/yii2',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                Yii::t('app', 'Telegram'),
+                                'https://t.me/yii_framework_in_english',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
                         </ul>
                     </div>
                     <div class="card-footer bg-transparent border-0">
-                        <?= Html::a('Yii Forum &raquo;', 'https://www.yiiframework.com/forum/', ['class' => 'btn btn-outline-secondary']) ?>
+                        <?= Html::a(
+                            'Yii Forum &raquo;',
+                            'https://www.yiiframework.com/forum/',
+                            ['class' => 'btn btn-outline-secondary'],
+                        ) ?>
                     </div>
                 </div>
             </div>
@@ -62,17 +122,52 @@
                     <div class="card-body">
                         <h2 class="h5"><?= Yii::t('app', 'Official Extensions') ?></h2>
 
-                        <p><?= Yii::t('app', 'Supercharge your app with battle-tested packages maintained by the core team.') ?></p>
+                        <p><?= Yii::t(
+                            'app',
+                            'Supercharge your app with battle-tested packages maintained by the core team.',
+                        ) ?></p>
 
                         <ul class="list-unstyled small">
-                            <li><?= Html::a('yii2-debug', 'https://www.yiiframework.com/extension/yiisoft/yii2-debug', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a('yii2-gii', 'https://www.yiiframework.com/extension/yiisoft/yii2-gii', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a('yii2-queue', 'https://www.yiiframework.com/extension/yiisoft/yii2-queue', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
-                            <li><?= Html::a('yii2-redis', 'https://www.yiiframework.com/extension/yiisoft/yii2-redis', ['target' => '_blank', 'rel' => 'noopener']) ?></li>
+                            <li><?= Html::a(
+                                'yii2-debug',
+                                'https://www.yiiframework.com/extension/yiisoft/yii2-debug',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                'yii2-gii',
+                                'https://www.yiiframework.com/extension/yiisoft/yii2-gii',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                'yii2-queue',
+                                'https://www.yiiframework.com/extension/yiisoft/yii2-queue',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
+                            <li><?= Html::a(
+                                'yii2-redis',
+                                'https://www.yiiframework.com/extension/yiisoft/yii2-redis',
+                                [
+                                    'rel' => 'noopener',
+                                    'target' => '_blank',
+                                ],
+                            ) ?></li>
                         </ul>
                     </div>
                     <div class="card-footer bg-transparent border-0">
-                        <?= Html::a('Yii Extensions &raquo;', 'https://www.yiiframework.com/extensions/', ['class' => 'btn btn-outline-secondary']) ?>
+                        <?= Html::a(
+                            'Yii Extensions &raquo;',
+                            'https://www.yiiframework.com/extensions/',
+                            ['class' => 'btn btn-outline-secondary'],
+                        ) ?>
                     </div>
                 </div>
             </div>
diff --git a/web/css/site.css b/web/css/site.css
index e9f8ab1dc..7948487be 100644
--- a/web/css/site.css
+++ b/web/css/site.css
@@ -1,6 +1,8 @@
 main > .container {
     padding: 70px 15px 20px;
-    height: 100%;
+    display: flex;
+    flex-direction: column;
+    min-height: 100%;
 }
 
 .not-set {
@@ -100,3 +102,42 @@ a.desc:after {
 [data-bs-theme="dark"] .site-contact img[src*="captcha"] {
     filter: invert(1) hue-rotate(180deg);
 }
+
+/* centered page layout: error, about, contact success */
+.site-index,
+.site-error,
+.site-about,
+.site-contact-success {
+    flex: 1;
+}
+
+.site-error .site-error-content,
+.site-about .site-about-content,
+.site-contact-success .site-contact-success-content {
+    width: 100%;
+    max-width: 90%;
+}
+
+@media (min-width: 576px) {
+    .site-error .site-error-content,
+    .site-about .site-about-content,
+    .site-contact-success .site-contact-success-content {
+        max-width: 80%;
+    }
+}
+
+@media (min-width: 768px) {
+    .site-error .site-error-content,
+    .site-about .site-about-content,
+    .site-contact-success .site-contact-success-content {
+        max-width: 60%;
+    }
+}
+
+@media (min-width: 992px) {
+    .site-error .site-error-content,
+    .site-about .site-about-content,
+    .site-contact-success .site-contact-success-content {
+        max-width: 50%;
+    }
+}
diff --git a/web/index-test.php b/web/index-test.php
index 7d8c65fcf..b673f6f5b 100644
--- a/web/index-test.php
+++ b/web/index-test.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // NOTE: Make sure this file is not accessible when deployed to production
 if (!in_array(@$_SERVER['REMOTE_ADDR'], ['127.0.0.1', '::1'])) {
     die('You are not allowed to access this file.');
diff --git a/web/index.php b/web/index.php
index 02d5e1da9..30fa40aaf 100644
--- a/web/index.php
+++ b/web/index.php
@@ -1,5 +1,7 @@
 <?php
 
+declare(strict_types=1);
+
 // comment out the following two lines when deployed to production
 defined('YII_DEBUG') or define('YII_DEBUG', true);
 defined('YII_ENV') or define('YII_ENV', 'dev');
diff --git a/widgets/Alert.php b/widgets/Alert.php
index 1302c1f29..f9e7514cd 100644
--- a/widgets/Alert.php
+++ b/widgets/Alert.php
@@ -1,8 +1,11 @@
 <?php
 
+declare(strict_types=1);
+
 namespace app\widgets;
 
 use Yii;
+use yii\bootstrap5\Alert as BootstrapAlert;
 
 /**
  * Alert widget renders a message from session flash. All flash messages are displayed
@@ -31,7 +34,7 @@ class Alert extends \yii\bootstrap5\Widget
      * - key: the name of the session flash variable
      * - value: the bootstrap alert type (i.e. danger, success, info, warning)
      */
-    public $alertTypes = [
+    public array $alertTypes = [
         'error'   => 'alert-danger',
         'danger'  => 'alert-danger',
         'success' => 'alert-success',
@@ -42,29 +45,32 @@ class Alert extends \yii\bootstrap5\Widget
      * @var array the options for rendering the close button tag.
      * Array will be passed to [[\yii\bootstrap\Alert::closeButton]].
      */
-    public $closeButton = [];
-
+    public array $closeButton = [];
 
     /**
      * {@inheritdoc}
      */
-    public function run()
+    public function run(): void
     {
         $session = Yii::$app->session;
+
         $appendClass = isset($this->options['class']) ? ' ' . $this->options['class'] : '';
 
         foreach (array_keys($this->alertTypes) as $type) {
             $flash = $session->getFlash($type);
 
             foreach ((array) $flash as $i => $message) {
-                echo \yii\bootstrap5\Alert::widget([
-                    'body' => $message,
-                    'closeButton' => $this->closeButton,
-                    'options' => array_merge($this->options, [
-                        'id' => $this->getId() . '-' . $type . '-' . $i,
-                        'class' => $this->alertTypes[$type] . $appendClass,
-                    ]),
-                ]);
+                echo BootstrapAlert::widget(
+                    [
+                        'body' => $message,
+                        'closeButton' => $this->closeButton,
+                        'options' => [
+                            ...$this->options,
+                            'id' => $this->getId() . '-' . $type . '-' . $i,
+                            'class' => $this->alertTypes[$type] . $appendClass
+                        ],
+                    ],
+                );
             }
 
             $session->removeFlash($type);