Change opacity of Image on mouseover

Hi, great design as always! One question. That’s not even a problem with your design, I’m just wondering if I can do the following: using “Inline CSS styles” on image settings I want to put there css class which will light up the image (only on mouseover) by adding transparency to it. Is this even possible just using Visual website editor? If it is not that easy, then don’t bother yourself ;) Thank you.