Changing width and height in angular-chart.js module

I'm using the angular module angular-chart.js. It is simple to work with and very smart. But I've noticed that I can't change the width and height of the charts. Somewhere I've read that I have to define the size of the chart as follows:

var vm = $scope;
vm.labels = [];
vm.data = [];

CrudService.getData(selDate).$promise.then(
     function (response) {
       angular.forEach(response, function (val) {
          val.datum = $filter('date')(val.datum, 'dd.MM.yyyy');
          vm.labels.push(val.datum);
          vm.data.push(val.grade);
       });

       vm.dataChart = [vm.data];

       /* This is the important part to define the size */
       vm.options = [
         {
            size: {
               height: 200,
               width: 400
            }
         }
       ];
       /************************************************/
    });

The view:

<canvas id="bar" 
        class="chart chart-bar" 
        chart-data="dataChart"
        chart-labels="labels"
        chart-click="onClick"
        chart-options="options">
</canvas>

Do anyone knows how to define the width and height in angular-chart.js ?

Ok I have tried this solution and it works.

        <canvas id="bar"
                height="100"
                width="100"
                class="chart chart-bar" 
                chart-data="dataChart"
                chart-labels="labels"
                chart-click="onClick"
                chart-options="options">
        </canvas>

Or defining the size as like a style in a CSS-class.