[Bug]: Using tailwindcssV4, @apply does not work properly in some scenarios

Version

System: windows11
Browsers:133.0.6943.142（正式版本） （64 位）
npmPackages:
"dependencies": {
  "vue": "^3.5.13"
},
"devDependencies": {
  "@rsbuild/core": "^1.2.16",
  "@rsbuild/plugin-sass": "^1.2.2",
  "@rsbuild/plugin-vue": "^1.0.7",
  "@tailwindcss/postcss": "^4.0.12",
  "tailwindcss": "^4.0.12"
}

Details

异常情况:

1. 使用pnpm create rsbuild@latest 初始化一个vue项目,
2. 按官方文档安装了tailwindcssV4：https://rsbuild.dev/zh/guide/basic/tailwindcss
3. 在项目中新增test.scss文件，文件内容如下:
   .test {
   @apply bg-red-500;
   }
4. 在入口文件index.js中引入 import './test.scss'
5. 启动项目，报错::× Error: Cannot apply unknown utility class: bg-red-500

正常情况:
1.在App.vue文件中的style添加以下样式代码:

<style lang="scss" scoped> .test { @apply bg-red-500 ; } </style>

2. 启动服务能正常加载样式

Reproduce link

无

Reproduce Steps

上面有详细步骤描述

[chenjiahan]

Have you tried to use the @apply in a CSS file?

See: https://rsbuild.dev/zh/guide/basic/tailwindcss#%E5%BC%95%E5%85%A5-css