js snippet to keep element the size of the viewable port. Note, this require a valid DOC type in the document.

viewport.js

$(document).ready(function(){
	set_size()
});

$(window).resize(function(){
	set_size();
});

function set_size(){
	var h = $(window).height(); 
	var w = $(window).width();

	var head = $('#header');
	head.height(h);
	head.width(w);
}