slideshow.io/static/css/viewer.css

body {
    margin: 0px;
}

#canvas-paint, #canvas-pdf {
    margin:auto;
    position:absolute;
    top:0;
    bottom:0;
    left:0;
    right:0;
    max-height:100%;
    max-width:100%;
    padding-bottom:0px;
    margin-bottom:0px;
}