html,
body {
    width: 100%;
    height: 100%;
    padding: 0;
    margin: 0;
    overflow: hidden;
}

#renderCanvas {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    display: block;
    font-size: 0;
    z-index: 0; /* Canvas ganz hinten */
}