AngularJS: ng-style or style

HTML

<body ng-app="myApp">
    <div ng-controller="myCtrl">
            
        <div class="boxClass" style="background: red"> style attribute</div>
        <br>
       
        <div class="boxClass" ng-style="getStyle(colorBg)"> set using ng style</div> 
        <br>
           
        <button ng-click="changeColour()">Click Me</button>
    </div>
</body>

CSS

.boxClass {
    width:200px;
    height:200px;
}

JavaScript

// declare a module
var myApp = this.angular.module('myApp', []);

// declare a controller
myApp.controller('myCtrl', function ($scope, $interval) {
    $scope.colorBg = "F0F000";
    
    $scope.getStyle = function(colour) {
        return {"background": "#" + colour};
    }
    
    $scope.changeColour = function() {
    		$scope.colorBg = "FFFFFF"
    }   
   
});