Gallery overlay

Hi,

presumably an easy question concerning the gallery:

I would like to change the overlay effect.
My overlay is a dark one, 3px bigger than the photo at the right side and bottom.

Instead of this I would like the photo just become a little bit lighter when hovering it (as in your galleries at html/galleries.html).

The code actually is:

<div class="masonry-thumbs grid-4 clearfix" data-lightbox="gallery">
	<a href="images/photo01.jpg" title="Margarita Vilsone, Soprano &copy; Aiga Redmane">
		<img src="images/photo01.jpg" alt="Gallery Image" />
		<div class="overlay">
			<div class="overlay-wrap">
				<i class="icon-line-plus"></i>
			</div>
		</div>
	</a>
</div>

Changes in the overlay classes do not work:

.overlay {
position: absolute;
top: 0;
left: 0;
width: 100%;
height: 100%;
}

.overlay .overlay-wrap,
.text-overlay {
opacity: 0;
position: relative;
width: 100%;
height: 100%;
background-color: rgba(0,0,0,0.6);
}

Seem to be not the right ones...

Thanks for your help in advance and regards,

Monika