* {
box-sizing: border-box;
}

div.gallery {
    display: flex;
    flex-wrap: wrap;
    justify-content: flex-start;
}

div.gallery-item {
    margin: 5px;
    border: 1px solid #ccc;
    width: calc(25% - 20px);
}

div.gallery-item:hover {
    border: 1px solid #777;
}

div.gallery-item img {
    width: 100%;
    height: auto;
}

div.gallery-item div.desc {
    padding: 15px;
    text-align: center;
}

@media only screen and (max-width: 768px) {
    div.gallery-item {
        width: calc(50% - 20px);
    }
}

@media only screen and (max-width: 480px) {
    div.gallery-item {
        width: calc(100% - 20px);
    }
}