style: add classnames

Author: andrewagain

src/component/App.js

@@ -19,7 +19,7 @@ class App extends React.Component {
 
   render() {
     return (
-      <div>
+      <div className="component-app">
         <Display
           value={this.state.next || this.state.total || '0'}
         />

src/component/Button.js

@@ -8,6 +8,7 @@ class Button extends React.Component {
   render() {
     return (
       <button
+        className="component-button"
         onClick={this.handleClick}
       >
         {this.props.name}

src/component/ButtonPanel.js

@@ -8,7 +8,7 @@ class ButtonPanel extends React.Component {
 
   render() {
     return (
-      <div>
+      <div className="component-button-panel">
         <div>
           <Button name="AC" clickHandler={this.handleClick} />
           <Button name="+/-" clickHandler={this.handleClick} />

src/component/Display.js

@@ -3,7 +3,7 @@ import React from 'react';
 class Display extends React.Component {
   render() {
     return (
-      <div>
+      <div className="component-display">
         <div>
           {this.props.value}
         </div>