vue-cli脚手架: vue create client创建的项目中使用postcss不生效

通过vue create client创建了一个前端项目，然后新建了一个Header.vue，里面的postcss写法编译虽然能过，但是不起作用，主要就是嵌套了！

求解答：

基本环境: mac os x : 10.12

[zcm@client 5]$node -v

v12.6.0

[zcm@client 6]$npm -v

6.9.0

[zcm@client 7]$vue -V

3.9.2

基本框架:


package.json:

{

  "name": "client",

  "version": "0.1.0",

  "private": true,

  "scripts": {

    "serve": "vue-cli-service serve",

    "build": "vue-cli-service build",

    "lint": "vue-cli-service lint"

  },

  "dependencies": {

    "core-js": "^2.6.5",

    "vue": "^2.6.10"

  },

  "devDependencies": {

    "@vue/cli-plugin-babel": "^3.10.0",

    "@vue/cli-plugin-eslint": "^3.10.0",

    "@vue/cli-service": "^3.10.0",

    "babel-eslint": "^10.0.1",

    "eslint": "^5.16.0",

    "eslint-plugin-vue": "^5.0.0",

    "postcss-preset-env": "^6.7.0",

    "vue-template-compiler": "^2.6.10"

  },

  "eslintConfig": {

    "root": true,

    "env": {

      "node": true

    },

    "extends": [

      "plugin:vue/essential",

      "eslint:recommended"

    ],

    "rules": {

      "no-console": "off"

    },

    "parserOptions": {

      "parser": "babel-eslint"

    }

  },

  "postcss": {

    "plugins": {

      "autoprefixer": {},

      "postcss-preset-env": {}

    }

  },

  "browserslist": [

    "> 1%",

    "last 2 versions"

  ]

}

babel.config.js:

module.exports = {

  presets: [

    '@vue/app'

  ]

}

./components/Header.vue:

<template>

    <div>

        <div class="top">

            <div>logo</div>

            <div>sign in / sign out</div>

        </div>

    </div>

</template>

<script>

export default {

    data: function() {

        return {

            name: 'joeblack2'

        }

    },



    props: [

        

    ],

}

</script>



<style lang="postcss" scoped>

    .top {

        display: flex;

        align-content: center;



        & :hover {

            color: #666;

        }

        div {

            /* border: 1px solid red; */

            color: green;

        }

    }

</style>

谢谢大家！

这个默认创建的工程里没有webpack.config.js，是不是因为采用了脚手架里默认的配置了！网上的文章看了一大堆，各有各的写法，而且是写在不同的配置文件里的，前提条件也没有讲的太明确 ，不知从哪下手！