// Function for centering a page. Specify the page height and base font size.

        function centerPage()
        {
            var pageheight = 600;
            var margin;
            var baseFontSize = 10;
            var height = pageheight + 2 * baseFontSize;
           
            if (window.innerHeight)
            {
                height = window.innerHeight;
            }
            
            else
            {
                if (document.documentElement.clientHeight)
                {
                    height = document.documentElement.clientHeight;
                }
                else
                {
                    if (document.body.offsetHeight) 
                    {
                        height = document.body.offsetHeight;
                    } 
                }
            }
            
            margin = (height - pageheight) / 2;
            
            if (margin < baseFontSize)
            {
                margin = baseFontSize;
            }
            
            margin = margin / baseFontSize;
            
            document.body.style.marginTop = margin + "em";
            document.body.style.marginBottom = margin + "em";
            
        }