.grid-sizer,
.grid-item { width: 22%; }

.gutter-sizer { width: 4%; }

.grid-item--width2 { width: 48%; }

.grid-item {
  margin-bottom: 15px;
}
.card {
  perspective: 1000px;
  background: none;
}

.card-inner {
  position: relative;
  transform-style: preserve-3d;
  transition: transform 0.999s;
}

.card:hover .card-inner {
  transform: rotateY(180deg);
}

.card-front,
.card-back {
  width: 100%;
  backface-visibility: hidden;
}

.card-front {
  transform: rotateY(0deg);
}

.card-back {
    border-radius: 0.375rem;
  background-color: #ccc;  
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  transform: rotateY(180deg);
}

.card-img-top {
    border-radius: 0.375rem;
}

@media screen and (max-width: 1200px) {
  .grid-sizer,
  .grid-item { width: 30%; }

  .grid-item--width2 { width: 63%; }

  .gutter-sizer { width: 5%; }
}

@media screen and (max-width: 750px) {
  .grid-sizer,
  .grid-item { width: 45%; }

  .grid-item--width2 { width: 97.5%; }

  .gutter-sizer { width: 10%; }
}
@media screen and (max-width: 350px) {
  .grid-sizer,
  .grid-item { width: 93%; }

  .gutter-sizer { width: 0%; }
}