#spinner {
    position: fixed;
    left: 0px;
    top: 0px;
    width: 100%;
    height: 100%;
    z-index: 9999;
    background-image: url('https://atscdn.azureedge.net/public/images/spinner.gif');
    background-color: #fff;
    background-position: center center;
    background-repeat: no-repeat;
}

.WebPartZoneDesignTime div#spinner {
    position: relative;
}