Separate index.css and App.css

src/App.css

@@ -1,8 +1,8 @@
-body {
-  background-color: #f5fcff;
+.App {
+  padding: 0px 20px;
 }
 
-.App--logo {
+.App-logo {
   animation: spin infinite 20s linear;
   border-radius: 50%;
   vertical-align: middle;

src/App.js

@@ -1,12 +1,12 @@
-import React from 'react';
 import './App.css';
+import React from 'react';
 import logo from './logo.png';
 
 export default function App() {
   return (
-    <div>
+    <div className="App">
       <h1>
-        Welcome to <img src={logo} className="App--logo" alt="logo" /> React
+        Welcome to <img src={logo} className="App-logo" alt="logo" /> React
       </h1>
       <p>
         To get started, edit <code>src/App.js</code> and save to reload.

src/index.css

@@ -0,0 +1,4 @@
+body {
+  background-color: #f5fcff;
+  font-family: sans-serif;
+}

src/index.js

@@ -1,3 +1,4 @@
+import './index.css';
 import React from 'react';
 import { render } from 'react-dom';
 import App from './App';