var min = 0.5;
var max = 2;
var elements, size;

function zoomIn() {
	elements = document.getElementsByTagName("body");
	for (var i = 0; i < elements.length; i++) {
		if (elements[i].style.fontSize) {
			size = parseFloat(elements[i].style.fontSize.replace("em", ""));
		} else {
			size = 1;
		}
		if (size < max) {
			size += 0.1;
		}
		elements[i].style.fontSize = size + "em";
	}
}

function zoomOut() {
	elements = document.getElementsByTagName("body");
	for (var i = 0; i < elements.length; i++) {
		if (elements[i].style.fontSize) {
			size = parseFloat(elements[i].style.fontSize.replace("em", ""));
		} else {
			size = 1;
		}
		if (size > min) {
			size -= 0.1;
		}
		elements[i].style.fontSize = size + "em";
	}
}