.gallery{
    display: flex;
    flex-wrap: wrap;
    margin: 0 0 50px 0;
    padding: 0;
}
.gallery-item{
    flex: 1 1 16.6667%;
    -ms-flex: 1 1 16.6667%;
}
.gallery img{
  width: 100%;
  height: 200px;
  object-fit: cover;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  margin: auto;
  padding: 2%;
}

@media screen and (max-width: 999px){
 .gallery-item{
    flex: 1 1 25%;
    -ms-flex: 1 1 25%;
}
.gallery img{
  width: 100%;
  height: 150px;
  object-fit: cover;
  top: 0;
  right: 0;
  bottom: 0;
  left: 0;
  margin: 5px;
  padding: 2%;
}   
}