after popup gets open header of the page also gets gray out

After opening popup or modal window background are getting grayout but the header section of the page is not getting grayout ,

i wanted to grayout header section also .

$mdDialog.show({

controller: userPRefrencesController,

templateUrl: '../App/Views/UserPrefrencesTable.html',

parent: angular.element(document.body),

targetEvent: ev,

clickOutsideToClose: false,

fullscreen: $scope.customFullscreen,

//windowTemplateUrl: 'modalWindowTemplte.html'

})

.then(function (answer) {

$scope.status = 'You said the information was "' + answer + '".';

}, function () {

$scope.status = 'You cancelled the dialog.';

});