Template:Gallery items/styles.css

@media screen {
	.gallery-items .gallerybox div.thumb {
		background-color: transparent !important;
	}
	.gallery-items .gallerybox .thumb img {
		background-color: transparent !important;
	}
	.gallery-items .gallerybox .thumb img:hover {
		background: url(//upload.wikimedia.org/wikipedia/commons/9/90/Checker-16x16.svg) repeat !important;
	}
}