var max = 24
var min = 8 
function upSize() { 
    size = parseInt(document.getElementById("content").style.fontSize) 
    if (size < max) { 
        size = size + 2 
    } 
    document.getElementById("content").style.fontSize = size + "px" 
} 

function downSize() { 
    size = parseInt(document.getElementById("content").style.fontSize) 
    if (size > min) { 
        size = size - 2 
    } 
    document.getElementById("content").style.fontSize = size + "px" 
}