AngularJS Training- Hello World

<html ng-app="app">
<head>
  <script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.15/angular.min.js"></script>
  <script src="script.js"></script>
</head>
<body>
  <div ng-controller='HelloController'>
    <p>{{greeting.text}}, World</p>
  </div>
  <input type="button" value="red color" ng-click="color='red'">
  <input type="button" value="black color" ng-click="color='black'">
  <input type="button" value="blue color" ng-click="color='blue'">
  <input type="button" value="font-weight" ng-click=font-weight='bold'">
  <button ng-click="size = size + 1">aA</button>
  <button ng-click="size = size - 1">Aa</button>
  <p></p>
  <textarea ng-style="{'color': color, 'font-size': size, 'font-weight': 'bold'}">
  </textarea>
</body>
</html>

angular.module('app', [])

.controller('HelloController', function($scope) {
  $scope.greeting = {};
  $scope.greeting.text = 'Hello';
  $scope.size = 12;
});

/* Styles go here */