AngularJS ngMouseover example with ngClass.

HTML

<div ng-app="myApp" ng-controller="MainCtrl">
    <div ng-class="getClass()" ng-mouseover="toggle()">Mouseover me!</div>
</div>

CSS

.red {
    background: red;
}

.blue {
    color: white;
    background: blue;
}

JavaScript

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

app.controller('MainCtrl', function($scope) {
    var showing = false;
    
    $scope.getClass = function() {
        if ( showing ) {
            return 'red';
        } else {
            return 'blue'
        }
    };
    
    $scope.toggle = function() {
        showing = !showing;
    };
});