diff --git a/extend.php b/extend.php
new file mode 100644
index 0000000..3b7c563
--- /dev/null
+++ b/extend.php
@@ -0,0 +1,35 @@
+<?php
+
+use Flarum\Extend;
+use Flarum\Api\Serializer\UserSerializer;
+use Flarum\User\User;
+use Illuminate\Contracts\View\Factory;
+
+return [
+    // 1. 给 UserSerializer 加字段 theme，方便前端读取
+    (new Extend\ApiSerializer(UserSerializer::class))
+        ->attribute('theme', fn ($serializer, User $user) => $user->getPreference('theme', 'default')),
+
+    // 2. 允许前端修改 theme
+    (new Extend\User())
+        ->registerPreference('theme', 'strval', 'default'),
+
+    // 3. 根据主题注入 CSS
+    (new Extend\Frontend('forum'))
+        ->css(function (Factory $view, User $user) {
+            $theme = $user->getPreference('theme', 'default');
+            // 只注入存在的文件
+            $path = "theme-switcher/less/{$theme}.less";
+            if (file_exists(__DIR__ . "/resources/less/{$theme}.less")) {
+                return $view->make('flarum.forum::frontend.content.css', [
+                    'css' => [$path]
+                ]);
+            }
+            return null;
+        }),
+
+    // 4. 设置页组件挂载
+    (new Extend\Frontend('forum'))
+        ->js(__DIR__ . '/js/dist/forum.js')
+        ->css(__DIR__ . '/resources/less/app.less'), // 公共样式（可选）
+];