CSS - memory game

.cards {
  width: 70%;
  height: 90vh;
  /* display each card in a grid */
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  grid-gap: 1em;
  margin: auto;
}

.card {
  background-color: gainsboro;
  height: 25vh;
  border-radius: 1em;
  /* center item */
  display: flex;
  align-items: center;
  justify-content: center;
  /* create space between img and border */
  padding: 0.5em;
}

.card > img {
  max-width: 100%;
  max-height: 100%;
}

.front {
  display: block;
}

.back {
  display: none;
}

.show {
  display: block;
}

.hide {
  display: none;
}

.card:hover {
  box-shadow: 3px 3px 5px lightskyblue;
}