vue Build multi-page CSS load redundant

[davedat]

Version

4.0.5

Reproduction link

http://127.0.0.1:8080/#/

Environment info

{
  "name": "html",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "serve": "vue-cli-service serve",
    "build": "vue-cli-service build"
  },
  "dependencies": {
    "babel-polyfill": "^6.26.0",
    "core-js": "^3.3.2",
    "view-design": "^4.0.2",
    "vue": "^2.6.10",
    "vue-router": "^3.1.3",
    "vuex": "^3.0.1"
  },
  "devDependencies": {
    "@vue/cli-plugin-babel": "^4.0.0",
    "@vue/cli-plugin-router": "^4.0.0",
    "@vue/cli-plugin-vuex": "^4.0.0",
    "@vue/cli-service": "^4.0.0",
    "vue-template-compiler": "^2.6.10"
  }
}

Steps to reproduce

// vue.config.js

module.exports = {
  outputDir:"../src/main/resources/static/",
  pages: { 
    admin: {
      entry: 'src/main.js',
      template: 'public/index.html',
      filename: 'index.html',
      title: 'admin'
    },
    mobile: {
      entry: 'src/mobile.js',
      template: 'public/mobile.html',
      filename: 'mobile.html',
      title: 'mobile',
    }
  }
}

// src/main.js

import Vue from 'vue'
import App from './App.vue'
import router from './router'
import store from './store'

import ViewUI from 'view-design'

/*** this iview.css will appear in bundle file  mobile.html  why?  i just want it in index.html ***/
import 'view-design/dist/styles/iview.css'

import 'babel-polyfill'

Vue.use(ViewUI);

Vue.config.productionTip = false

new Vue({
  router,
  store,
  render: h => h(App)
}).$mount('#app')

// src/mobile.js

import Vue from 'vue'
import App from './App.vue'
import router from './router/mobile'
import store from './store/mobile'

/****  here have no css file import ****/

Vue.config.productionTip = false

new Vue({
  router,
  store,
  render: h => h(App)
}).$mount('#app')

What is expected?

bundle file mobile.html have no css iview.css import

What is actually happening?

bundle file mobile.html have css iview.css import
i just want it in index.html

when i run npm run serve it working
but npm run build
how to fix it ?