Add Divi Gallery Overlay - Part 3

/* Hides the slider arrows and controller (bullets) on the thumbnail */
.et_pb_gallery .et-pb-slider-arrows,  .et_pb_gallery .et-pb-controllers  {display: none; }
/* Creates the fade effect to the hovering that eases in the opacity change */
.et_pb_gallery_image a {transition: all 0.5s ease;  }
/* This addes the plus icon that displays on top of the thumbnail when it is hovered and makes it invisible when it is not hovered*/
.et_pb_gallery_image a .overlay {position: absolute; top: 37%; left: 40%; width: 50px !important; height: 50px !important; background: url(your-icon-image.png)  no-repeat !important; z-index: 99999999999; opacity:0;}
/* This changes the opacity of the thumbnail when it is hovered */
.et_pb_gallery_image a:hover img {opacity: 0.5; transition: all 0.5s ease;  }
/* This makes the icon appear when the thumbnail is hovered */
.et_pb_gallery_image a:hover .overlay {opacity:1 !important;}