AngularJS: different types of ng-class & class

HTML

<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.3.0-rc.1/angular.min.js"></script>
<div
    ng-controller="MainCtrl"
    class="just-a-class color-{{ data.color }}"
    ng-class="(data.size > 10) ? 'font-large' : 'font-small'"


>
    
    Lorem ipsum dolor sit amet.
    
    
    
</div>

SCSS

.color-red { background: red;}

.font-small { font-size: 1em; }
.font-large { font-size: 3em; }

JavaScript

var app = angular.module("app", []);

app.controller('MainCtrl', function($scope){

   $scope.data = {
    color: "red",
    size: 10
};

});