* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
.middle {
  /*   */
  margin-left: 50%;
  transform: translateX(-50%);
}

main {
  margin-top: 100px;
}

.flip-card {
  background-color: transparent;
  width: 300px;
  height: 300px;
  perspective: 1000px;
  margin: 1rem;
}

.flip-card-inner {
  position: relative;
  width: 100%;
  height: 100%;
  text-align: center;
  transition: transform 0.6s;
  transform-style: preserve-3d;
  box-shadow: 0 4px 8px 0 rgba(0, 0, 0, 0.2);
}

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

.flip-card-front,
.flip-card-back {
  position: absolute;
  width: 100%;
  height: 100%;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
}

.flip-card-front {
  background-color: #bbb;
  color: black;
}

.flip-card-back {
  background-color: #2980b9;
  color: white;
  transform: rotateY(180deg);
}