style: import css

src/component/App.js

@@ -2,6 +2,7 @@ import React from 'react';
 import Display from './Display';
 import ButtonPanel from './ButtonPanel';
 import calculate from '../logic/calculate';
+import './App.css';
 
 class App extends React.Component {
   constructor(props) {

src/component/Button.js

@@ -1,4 +1,5 @@
 import React from 'react';
+import './Button.css';
 
 class Button extends React.Component {
   handleClick = () => {

src/component/ButtonPanel.js

@@ -1,5 +1,6 @@
 import React from 'react';
 import Button from './Button';
+import './ButtonPanel.css';
 
 class ButtonPanel extends React.Component {
   handleClick = (buttonName) => {

src/component/Display.js

@@ -1,4 +1,5 @@
 import React from 'react';
+import './Display.css';
 
 class Display extends React.Component {
   render() {