another option is to put a pop-up note (using css) on your page instead of buttons to change font sizes
Your post was not in plain English.
So now what you are saying is to pop up with a tool tip explaining to your users to increase the font size on the page through the zoom feature within the browser.
And if you look at your post closely, you will notice that it was kind of hard to understand.
another option is to put a pop-up note (using css) on your page instead of buttons TO CHANGE FONT SIZES
I guess this was all just a misunderstanding then.