Switch theme's banner when viewed on mobile devices.

I've been using some custom css to switch the banner of my website to one that is more mobile friendly when viewed on mobile devices. I recently switched themes and the css code stopped working. Can you help me figure out what changes I need to make to get it working in the new theme? I've included the css below.

/* custom from Panos at wpmudev, to switch theme's banner when viewed on mobile devices 5.25.16*/

@media screen and (max-width: 960px) {
#top-bg .top-bg-inner a img{
		content:url("https://cincinnati.unitedresourceconnection.com/wp-content/uploads/2016/04/urclogindraft.png") !important;
	}
}