Hi yvan01,
You can add the following CSS code to your site: Backend > Site template styles > ja agrivita > Tools > Custom CSS:
#fancybox-loading {
position: fixed;
top: 50%;
left: 50%;
width: 40px;
height: 40px;
margin-top: -20px;
margin-left: -20px;
cursor: pointer;
overflow: hidden !important;
z-index: 1104;
display: none;
}