var min = 10;
var max = 18;
function increasefont() {
	var body = document.getElementsByTagName('body')[0];
	if(body.style.fontSize) {
		var size = parseInt(body.style.fontSize.replace("px",""));
	} else {
		var size = 12;
	}
	if(size != max) {
		size += 1;
	}
	body.style.fontSize = size+"px";
}

function decreasefont() {
	var body = document.getElementsByTagName('body')[0];
	if(body.style.fontSize) {
		var size = parseInt(body.style.fontSize.replace("px",""));
	} else {
		var size = 12;
	}
	if(size != min) {
		size -= 1;
	}
	body.style.fontSize = size+"px";
}