function animate_box() {  
        var offset = 0; /* set this to the starting margin-top in the css */  
        var element = document.getElementById('animate_box');  
      
        if(element) {  
            var top = Number(String(element.style.marginTop).substring(0, String(element.style.marginTop).indexOf('px')));  
      
            try {  
                if(document.body.scrollTop > 0) {  
                    var difference = (document.body.scrollTop + offset);  
                } else if(document.documentElement.scrollTop > 0) {  
                    var difference = (document.documentElement.scrollTop + offset);  
                } else {  
                    var difference = offset;  
                }  
            } catch(e) {  
                var difference = offset;  
            }  
      
            difference = difference - top;  
      
            if(difference > 0) {  
                element.style.marginTop = (top + Math.abs(Math.ceil(difference / 10))) + 'px';  
            } else if(difference < 0) {  
                element.style.marginTop = (top - Math.abs(Math.ceil(difference / 10))) + 'px';  
            }  
        }  
    }  
    window.setInterval(animate_box, 50);