problem description
I created a hello-world project using vue-cli version 3.0:
vue create hello-world
// I found that it enabled the service
by using vue serve .
 now I want to join postcss, and find that the  pkg.json  generated by it has already written this configuration: 
"postcss": {
  "plugins": {
    "autoprefixer": {}
  }
},this is not like the webpack configuration I used earlier.
 how do I configure postcss, now if I want to join it? Does 
 still need to be configured in the same way as the original webpack? 
related codes
 / / Please paste the code text below (do not replace the code with pictures) 
 this is the pkg.json content after the project is created: 
{
  "name": "hello-world",
  "version": "0.1.0",
  "private": true,
  "scripts": {
    "serve": "vue-cli-service serve",
    "build": "vue-cli-service build",
    "lint": "vue-cli-service lint"
  },
  "dependencies": {
    "vue": "^2.5.16"
  },
  "devDependencies": {
    "@vue/cli-plugin-babel": "^3.0.0-rc.9",
    "@vue/cli-plugin-eslint": "^3.0.0-rc.9",
    "@vue/cli-service": "^3.0.0-rc.9",
    "vue-template-compiler": "^2.5.16"
  },
  "eslintConfig": {
    "root": true,
    "env": {
      "node": true
    },
    "extends": [
      "plugin:vue/essential",
      "eslint:recommended"
    ],
    "rules": {},
    "parserOptions": {
      "parser": "babel-eslint"
    }
  },
  "postcss": {
    "plugins": {
      "autoprefixer": {}
    }
  },
  "browserslist": [
    "> 1%",
    "last 2 versions",
    "not ie <= 8"
  ]
}
Thank you!
