.img-group {
display: flex;
justify-content: center;
}

.img-group img {
margin: 30px 30px 0;
}

@media only screen and (max-width: 768px) {
.img-group {
flex-direction: column;
display: inline-flex;
}

.img-group img {
margin: 30px auto 0;
}
}