function large() {
	document.body.style.fontSize = "16px";
	document.getElementById("nav1").className = "nav1";
	document.getElementById("nav2").className = "nav2_ac";
}
function middle() { 
	document.body.style.fontSize = "13px";
	document.getElementById("nav1").className = "nav1_ac";
	document.getElementById("nav2").className = "nav2";
}