How to put logo in header

Hello, I’m trying to figure out how to put a logo image in the upper left hand corner of this website, next to the banner ad and above the “register / login” links.

https://www.killerbusinessopportunities.com

There is a section in the stylesheet under the header section that reads:

.logo {
	background: url(images/logo.png) no-repeat;
	float: left;
	width: 240px;
	height: 90px;
	margin: 0;
	padding: 0;
}

I have put the full URL of the logo in url( ) but it still doesn’t show up.

I don’t understand, the logo is the perfect size and this seems like exactly where to edit the code to place it there. So why isn’t it showing up?

Thanks