在组件中引用
import React,{Component} from 'react';
import Hello from './components/Hello'
import Welcome from './components/Welcome'
export default class App extends Component{
  render(){
    return (
      <div>
        <Hello/>
        <Welcome/>
      </div>
    )
  }
}

将index.css改成index.module.css,将样式文件转换成一个模板文件
import hello from './index.module.css'
import { Component } from 'react'
export default class Welcome extends Component{
  render() {
    return (
      <div className={hello.title}>Hello</div>
    )
  }
}