diff --git a/CHANGELOG.md b/CHANGELOG.md
index 0fec7611..2d9a632e 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -26,6 +26,8 @@
 * fix [Flasher] Fix NotificationStorageMethods::resolveResourceName() return type from ?string to string (never returns null)
 * fix [Flasher] Fix parameter name inconsistency in NotificationBuilderInterface::options() - changed $merge to $append to match implementation
 * fix [Flasher] Add type validation for callable presenter return values in ResponseManager with descriptive error messages
+* fix [Flasher] Fix FlasherPlugin::normalizePlugins() losing scripts/styles when both top-level and plugin-level configs are provided - replaced array union operator with array_merge
+* fix [Flasher] Simplify FlasherPlugin::normalizeFlashBag() by replacing redundant array union with direct array_merge
 
 ## [v2.1.3](https://github.com/php-flasher/php-flasher/compare/v2.1.2...v2.1.3) - 2025-01-25
 
diff --git a/src/Prime/Plugin/FlasherPlugin.php b/src/Prime/Plugin/FlasherPlugin.php
index f0a56d49..d4278658 100644
--- a/src/Prime/Plugin/FlasherPlugin.php
+++ b/src/Prime/Plugin/FlasherPlugin.php
@@ -127,18 +127,24 @@ final class FlasherPlugin extends Plugin
         }
 
         if (!empty($config['scripts'])) {
-            $config['plugins']['flasher']['scripts'] ??= [];
-            $config['plugins']['flasher']['scripts'] += $config['scripts'];
+            $config['plugins']['flasher']['scripts'] = array_merge(
+                $config['plugins']['flasher']['scripts'] ?? [],
+                $config['scripts']
+            );
         }
 
         if (!empty($config['styles'])) {
-            $config['plugins']['flasher']['styles'] ??= [];
-            $config['plugins']['flasher']['styles'] += $config['styles'];
+            $config['plugins']['flasher']['styles'] = array_merge(
+                $config['plugins']['flasher']['styles'] ?? [],
+                $config['styles']
+            );
         }
 
         if (!empty($config['options'])) {
-            $config['plugins']['flasher']['options'] ??= [];
-            $config['plugins']['flasher']['options'] += $config['options'];
+            $config['plugins']['flasher']['options'] = array_merge(
+                $config['options'],
+                $config['plugins']['flasher']['options'] ?? []
+            );
         }
 
         foreach ($config['plugins'] as $name => $options) {
@@ -345,7 +351,7 @@ final class FlasherPlugin extends Plugin
             return $config;
         }
 
-        $config['flash_bag'] += array_merge($mapping, $config['flash_bag']);
+        $config['flash_bag'] = array_merge($mapping, $config['flash_bag']);
 
         return $config;
     }
diff --git a/tests/Prime/Plugin/FlasherPluginTest.php b/tests/Prime/Plugin/FlasherPluginTest.php
index f9daeb13..b07ba4c8 100644
--- a/tests/Prime/Plugin/FlasherPluginTest.php
+++ b/tests/Prime/Plugin/FlasherPluginTest.php
@@ -406,4 +406,57 @@ final class FlasherPluginTest extends TestCase
         $plugin = new FlasherPlugin();
         $this->assertSame([], $plugin->getOptions());
     }
+
+    public function testNormalizeConfigMergesTopLevelAndPluginLevelScripts(): void
+    {
+        $plugin = new FlasherPlugin();
+        $config = $plugin->normalizeConfig([
+            'scripts' => ['/top-level.js'],
+            'plugins' => [
+                'flasher' => [
+                    'scripts' => ['/plugin-level.js'],
+                ],
+            ],
+        ]);
+
+        // Both scripts should be present - plugin-level first, then top-level
+        $this->assertCount(2, $config['plugins']['flasher']['scripts']);
+        $this->assertContains('/plugin-level.js', $config['plugins']['flasher']['scripts']);
+        $this->assertContains('/top-level.js', $config['plugins']['flasher']['scripts']);
+    }
+
+    public function testNormalizeConfigMergesTopLevelAndPluginLevelStyles(): void
+    {
+        $plugin = new FlasherPlugin();
+        $config = $plugin->normalizeConfig([
+            'styles' => ['/top-level.css'],
+            'plugins' => [
+                'flasher' => [
+                    'styles' => ['/plugin-level.css'],
+                ],
+            ],
+        ]);
+
+        // Both styles should be present
+        $this->assertContains('/plugin-level.css', $config['plugins']['flasher']['styles']);
+        $this->assertContains('/top-level.css', $config['plugins']['flasher']['styles']);
+    }
+
+    public function testNormalizeConfigMergesOptionsWithPluginLevelOverride(): void
+    {
+        $plugin = new FlasherPlugin();
+        $config = $plugin->normalizeConfig([
+            'options' => ['timeout' => 5000, 'position' => 'top-right'],
+            'plugins' => [
+                'flasher' => [
+                    'options' => ['timeout' => 3000],
+                ],
+            ],
+        ]);
+
+        // Plugin-level timeout should override top-level
+        $this->assertSame(3000, $config['plugins']['flasher']['options']['timeout']);
+        // Top-level position should be preserved as default
+        $this->assertSame('top-right', $config['plugins']['flasher']['options']['position']);
+    }
 }