document.observe("dom:loaded", function () {

	$('overlay').setStyle({
        width: document.viewport.getWidth() + 'px',
        height: document.viewport.getHeight() + 'px'
    });

    var top = 0;
    var left = (document.viewport.getWidth() - 792) / 2;
    
    $('opp').setStyle({
      top: top + 'px',
      left:  left + 'px'
    });
    
    $('oppbtn').observe('click', function(){
        $('overlay').show();
        $('opp').show();
    });
    
    $('closeOpp').observe('click', function(){
        $('overlay').hide();
        $('opp').hide();
    });
});