Iframe background,modyfing

Hi ,

With this code i cant set a background ,

<iframe src="https://app.databox.com/datawall/e8c95f383a6cf2d526f95b28487bc5d" width="1280" height="720" frameborder="0"></iframe>

<style>
body{
  background-image: url('https://i.goopics.net/kxekcg.jpg');
  background-repeat: no-repeat;
  background-size: cover;
}
</style>

Someone already find out something or miro is just not friendly with iframe background ? 

My goal is to replace the image that Miro gives when you put an iframe code . 

Thanks .