.theme-choc_ns.slider-wrapper {
    position:relative;
    width:246px; /* Change this to your images width */
    height:350px; /* Change this to your images height */
    background:url(images/loading.gif) no-repeat 50% 50%;
}

.theme-choc_ns .nivoSlider {
    position:relative;
    width:246px;
    height:350px;
    margin-left:0px;
    background:url(loading.gif) no-repeat 50% 50%;
}