Calling featured image through CSS on Menu

I am using twnty thirteen as the base to build my theme on.

On my navbar, I have an image in the background. I want this image to chnage from one page to another. For this I intend to use the featured image. How can I change the background:image attribute to call from featured image of the particular page, instead of the URL image that it is calling in the sample code below.

.navbar {
	background-color: #f7f5e7;
	margin: 0 auto;
	max-width: 1600px;
	width: 100%;
	height: 209px;
	background-image: url(http://localhost/wordpress/wp-content/uploads/2015/08/career.jpg);
}