I checked the demo site and looks like the icon is very much centered (see screenshot at the end of the post). Pls see here –
https://www.livemeshthemes.com/appdev/portfolio-shortcodes/
Not sure if something changed in your site. BTW, the styling is present in the file
div.pp_default .pp_loaderIcon { background: url(../images/prettyPhoto/default/loader.gif) center center no-repeat; } /* Loader icon */
You can tweak the background position a bit and see if that makes a difference. If that does not help, pls see if tweaking the margin in the below CSS at line number 499 of the same file helps –
.pp_loaderIcon {
display: block;
height: 24px;
left: 50%;
margin: -12px 0 0 -12px;
position: absolute;
top: 50%;
width: 24px;
}
To locate in firebug, pls see screenshot below –