function changeFontSize(direction, step) {
    var min = 8;
    var max = 18;

    var p = document.getElementsByTagName('p');
    for (i = 0; i < p.length; i++) {
        if (p[i].style.fontSize) {
            var s = parseInt(p[i].style.fontSize.replace("px", ""));
        } else {
            var s = 12;
        }
        if ((direction == 'down' && s != min) || (direction == 'up' && s != max)) {
            s = s + step;
        }
        p[i].style.fontSize = s + "px"
    }
    var ul = document.getElementsByTagName('ul');
    for (i = 0; i < ul.length; i++) {
        if (ul[i].style.fontSize) {
            var s = parseInt(ul[i].style.fontSize.replace("px", ""));
        } else {
            var s = 12;
        }
        if ((direction == 'down' && s != min) || (direction == 'up' && s != max)) {
            s = s + step;
        }
        ul[i].style.fontSize = s + "px"
    }
}