Demo : https://suctreviet.123.st/html-h17.htm


#top-bottom_middle {
position:fixed;
_position:absolute;
bottom:5px;
right:5px;
clip:inherit;
_top:expres​sion(document.documentElement.scrollTop+
document.documentElement.clientHeight-this.clientHeight);
_left:expres​sion(document.documentElement.scrollLeft+ document.documentElement.clientWidth - offsetWidth);
}


var maxWidth = (document.body.clientWidth);
var maxHeight = (document.body.clientHeight);