Openstreetmap add css class to marker

Question

I'm using OpenLayers and I want to add a specific CSS class to highlight a marker. The marker is a .png image, and I can't find the propper way to add the css class to modify its style

Here is an example of the same image with and without style. I want to add in the map the stylished marker

http://jsfiddle.net/Ljq79s85/

var myStyle = new ol.style.Style({
    image: new ol.style.Icon({
       src: 'push_pin.png'
    })
});