var min=8;
var max=24;
function increaseFontSize() {
    var p = Ext.select('body, p', true);
    Ext.each(p.elements, function(item, index, allItems){
      if(item.getStyle('fontSize')) {
        var s = parseInt(parseInt(item.getStyle('fontSize'), 10));
      }else{
        var s = 12;
      }
      if(s!=max) {
        s += 1;
      }
      item.setStyle('fontSize', s+"px");
    });
}
function decreaseFontSize() {
    var p = Ext.select('body, p', true);
    Ext.each(p.elements, function(item, index, allItems){
      if(item.getStyle('fontSize')) {
        var s = parseInt(parseInt(item.getStyle('fontSize'), 10));
      }else{
        var s = 12;
      }
      if(s!=min) {
        s -= 1;
      }
      item.setStyle('fontSize', s+"px");
    });
}