function showBox(){     
    document.getElementById('overlay').style.display = "block";     
    center('box');     
    return false; 
    } 
    
function hideBox(){     
    document.getElementById('box').style.display = "none";     
    document.getElementById('overlay').style.display = "none";     
    return false; 
    } 
    
function center(element){     
    try{
        element = document.getElementById(element);
        }
    catch(e){         
        return;     
        }     
    var my_width = 0;     
    var my_height = 0;     
    if ( typeof( window.innerWidth ) == 'number' ){         
        my_width = window.innerWidth;         
        my_height = window.innerHeight;     
        }
    else if ( document.documentElement && ( document.documentElement.clientWidth || document.documentElement.clientHeight ) ){        
        my_width = document.documentElement.clientWidth;         
        my_height = document.documentElement.clientHeight;     
        }     
    else if ( document.body && ( document.body.clientWidth || document.body.clientHeight ) ){         
        my_width = document.body.clientWidth;         
        my_height = document.body.clientHeight;     
        }     
    element.style.position = 'absolute';     
    element.style.zIndex = 99;     
    var scrollY = 0;     
    
    if ( document.documentElement && document.documentElement.scrollTop ){         
        scrollY = document.documentElement.scrollTop;     
        }
    else if ( document.body && document.body.scrollTop ){         
        scrollY = document.body.scrollTop;     
        }
    else if ( window.pageYOffset ){         
        scrollY = window.pageYOffset;     
        }
    else if ( window.scrollY ){         
        scrollY = window.scrollY;     
        }     
        
    var elementDimensions = Element.getDimensions(element);     
    var setX = ( my_width - elementDimensions.width ) / 2;     
    var setY = ( my_height - elementDimensions.height ) / 2 + scrollY;     
    setX = ( setX < 0 ) ? 0 : setX;     
    setY = ( setY < 0 ) ? 0 : setY;     
    element.style.left = setX + "px";     
    element.style.top = setY + "px";     
    element.style.display = 'block'; 
    
    }