styles.css

body {
  height: 100vh;
  margin: 0;
}

#app {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  padding: 12px;
}

.card {
  width: 200px;
  height: 300px;
  perspective: 1000px;
  margin: 12px;
}

.card:hover {
  cursor: pointer;

  .card-inner {
    border-color: #cccccc;
    box-shadow: 0 0 10px rgba(0, 0, 0, 0.16);
  }
}

.card:focus {
  outline: none;
  
  .card-inner {
    border-color: #666666;
  }
}

.card:focus, .card:hover {
  .card-inner {
    border-width: 2px;
    margin: -1px;
  }
}

.card-inner {
  width: 100%;
  height: 100%;
  position: absolute;
  transform-style: preserve-3d;
  border: 1px solid #dddddd;
  border-radius: 6px;
  box-shadow: 0 0 6px rgba(0, 0, 0, 0.1);
  transition: border-color 0.3s, box-shadow 0.3s, transform 0.6s;
}

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

.face {
  width: 100%;
  height: 100%;
  position: absolute;
  backface-visibility: hidden;
  display: flex;
  align-items: center;
  justify-content: center;
  font-size: 18px;
}

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

.back {
  transform: rotateY(180deg);
}