var agt = navigator.userAgent.toLowerCase();
var is_ie = ((agt.indexOf("msie") != -1) && (agt.indexOf("opera") == -1));


function on_resize() {
	try {
		set_heights();
	}
	catch (er) {}
}

function set_heights() {
	try {
		var pageHeight = (window.innerHeight ? window.innerHeight : document.documentElement.clientHeight);
	    var pageWidth = (window.innerWidth ? window.innerWidth : document.documentElement.clientWidth);
       
        if ((pageWidth - 310 - 30 - 60) > 0) { 
            if ((pageWidth - 310 - 30 - 60) < 550) var boxContentWidth = (pageWidth - 310 - 30 - 60) + 'px';
            else var boxContentWidth = '490px';
		    document.getElementById('boxTopCenter').style.width = boxContentWidth;
        }
        if ((pageHeight - 100 - 20 - 60) > 0) { 
            var boxContentHeight = (pageHeight - 100 - 20 - 60) + 'px';
            document.getElementById('boxTopCenter').style.height = boxContentHeight;
        }
	}
	catch (err) {
		alert('Fout bij resizen: ' + err);
	}
}