wp geo-mashup remove margin from googlev3 infowindow

I need to remove the right and bottom margin from googlemap infowindow on my Geo-mashup wp plugin map.

I have installed the geo-mashup-custom plugin addon, created a file called custom-googlev3.js and inserted the following code.

GeoMashup.addAction( 'loadedMap', function ( properties, map ) {

google.maps.Event.addListener(infowindow, 'domready', function() {

   /* The DIV we want to change is above the .gm-style-iw DIV.
    * target the div through .gm-style-iw and .prev().
    */
   var iwBackground = jQuery('.gm-style-iw').prev();

   // Remove the background shadow DIV
   iwBackground.children(':nth-child(2)').css({'display' : 'none'});

   // Remove the white background DIV
   iwBackground.children(':nth-child(4)').css({'display' : 'none'});

   });
});

I found the above code from a guide here: http://en.marnoto.com/2014/09/5-formas-de-personalizar-infowindow.html but I am unable to use the code it provides in geomashp. I tried to implement fiddling with solution from other posts I found but its not working.

Any help really appreciated.