function show_pres()
{
	document.getElementById('title').style.display	= "none";
	document.getElementById('pre').style.display	= "none";
	document.getElementById('page').style.display	= "none";
	document.getElementById('nav').style.display	= "none";
	document.getElementById('pres').style.display	= "block";


	document.getElementById('background-page').style.background = "url('imgs/middle_blu.png')";
	document.getElementById('bottom').style.background = "url('imgs/bottom_blu.png')";
}