Content till footer

Hi I have made a sticky footer, but now the content of my website isn’t long enough. I want the middle of the website white till the footer, also if there’s not enough content. Now when I haven’t enough content the background stops after this content. How can I make the white background going down till the footer?

I use prestashop twentythirteen.

I thought it was site or site-main, but this doesn’t work:

.site {
	background-color: #fff;
	border-left: 1px solid #b3b3b3;
	border-right: 1px solid #b3b3b3;
	margin: 0 auto;
	max-width: 990px;
	width: 100%;
	height: 100%;
	position: static;
	bottom:150px;
}

.site-main {
		height: 100%;
	bottom:150px;
}

Thanks in advance!