.thumbnail {
  margin-left: auto;
  margin-right: auto;
}
.thumbnail .caption {
  margin-top: 31px;
}
.thumbnail3 {
  max-width: 270px;
}
.thumbnail4 {
  max-width: 370px;
}
.thumbnail6 {
  max-width: 570px;
}
@media (max-width: 991px) {
  .thumbnail6 {
    max-width: 370px;
  }
}