Edit in JSFiddle

Result
JavaScript
HTML
CSS

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

//Toggle Class
app.controller("myController", function($scope){	    
    $scope.class = "defaultClass";
    
    $scope.toggleClass = function(){
        if ($scope.class === "defaultClass")
            $scope.class = "newClass";
        else
            $scope.class = "defaultClass";
    };
});

<body ng-app="myApp" ng-controller="myController">
<div ng-class="class">Current class is: {{class}}</div>
<button ng-click="toggleClass()">Toggle Class</button>
</body>

div{ padding: 10px; color: #fff; }
.defaultClass{ background: #148fa1; }
.newClass { background: #2e7cb8; }