Utilizando GlobalStyles com styled-components

App.js

import React, { Component, Fragment } from 'react';
import GlobalStyle from './styles/GlobalStyles';
import Routes from './routes';

class App extends Component {
  state = {};

  render() {
    return (
      <Fragment>
        <GlobalStyle />
        <Routes />
      </Fragment>
    );
  }
}

export default App;

GlobalStyles.js

import { createGlobalStyle } from "styled-components";

const GlobalStyle = createGlobalStyle`
  * {
    padding: 0;
    margin: 0;
    outline: 0;

  }

  html, body {
    height: 100%;
    width: 100%;
    background: #f7f7f7;


    text-rendering: optimizeLegibility !important;
    -webkit-font-smoothing: antialiased !important;
    -moz-osx-font-smoothing: grayscale !important;
  }
  
  div#root{
    width: 100%;
    height: 100%;
  }

  input {
    outline: 0;
  }
`;

export default GlobalStyle;