Here is the code I used to make my gallery images hover
.gallery-caption {
position: absolute;
top: 0;
left: 0;
background-color: rgb(134, 137, 140);/* overlay color */
height: 100%;
max-width: unset;
padding: 0;
opacity: 0;
}
.gallery-caption-wrapper {
text-align: center;
color : white;
}
.gallery-caption-content {
font-size: 2rem !important; /* caption font size */
color: White; /*caption font color */
}
.gallery-grid-item {
position: relative;
color: white;
}
.gallery-grid-item:hover .gallery-caption {
opacity: 1;
}
.gallery-caption-grid-simple {
transition-delay: 0ms;
}