In your 'PowerGallery100/galleries/ribbon_fullsize/css/dark.css' try adding the 'position:relative' attribute to both .pg-rf .fullsize and .pg-rf .fullsize .loader styles:
/* fullsize image
--------------------------------------------------*/
.pg-rf .fullsize {
background-color: #303030;
border-color: #000;
position:relative;
}
.pg-rf .fullsize img {
}
.pg-rf .fullsize .loader {
color: #474747;
position:relative;
}
Incidentally, - although probably nothing to do with your immediate problem, you have a superfluous <html> in the Head area of your document:
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<html>
The third line: <html> can be removed.