https://www.modricainfo.com/wp-content/plugins/wp-font-resizer/js/fontResizer.js

1jQuery.noConflict();
2jQuery(function($) {	
3	function changeSize(element,size)
4	{
5		var fsize;
6		var current=parseInt(element.css('font-size'));
7		if(size=="smaller")
8		{
9			fsize=current-2;
10			if(fsize>=10)
11			{
12				element.css('font-size',fsize+'px');
13			}
14		}
15		if(size=="bigger")
16		{
17			fsize=current+2;
18			if(fsize<=40)
19			{
20				element.css('font-size',fsize+'px');
21			}
22		}	
23	}
24
25	$('.plusfont').on('click',function(){
26		changeSize($('body'),'bigger');
27	})
28	$('.minusfont').on('click',function(){
29		changeSize($('body'),'smaller');
30	})
31	$('.reloadfont').on('click',function(){
32		$('html body').css('font-size','');
33	})
34});