Add a hover effect to Wordpress post thumbnails

Hi :) I have a Wordpress site with some post thumbnails on it here - [login to view URL] (under the "Press" heading). If you hover over the Wine image, you'll see it has a black overlay with text. This text is the post title. There are two images here that I've pulled using Advanced Custom Fields - one is the thumbnail, and the other is the large image that's linked from the thumbnail (opens in a lightbox). What I need is for that hover effect on the Wine image to appear on all images. I'm altering someone else's code and having trouble figuring it out! Please bid only if you can begin work immediately. Anna