:root {
  --book-width: 50vh;
  --book-height: 75vh;
  --book-spine-width: 25px;
}

.book-container {
  perspective: 600px;
}

@keyframes initAnimation {
  0% {
    transform: rotateY(0deg);
  }
  100% {
    transform: rotateY(-20deg);
  }
}

.book {
  width: var(--book-width);
  height: var(--book-height);
  position: relative;
  transform-style: preserve-3d;
  transform: rotateY(-20deg);
  transition: 1s ease;
  animation: 1s ease 0s 1 initAnimation;
}

.book-container:hover .book, 
.book-container:focus .book {
  transform: rotateY(0deg);
}

.book > :first-child {
  position: absolute;
  top: 0;
  left: 0;
  background-color: red;
  width: var(--book-width);
  height: var(--book-height);
  transform: translateZ(12.5px);
  background-color: #01060f;
  border-radius: 0 0px 0px 0;
}

.book::before {
  position: absolute;
  content: ' ';
  background-color: blue;
  left: 0;
  top: 2px;
  width: 23px;
  height: 346px;
  transform: translateX(185.5px) rotateY(90deg);
  background: linear-gradient(90deg, 
    #fff 0%,
    #f9f9f9 5%,
    #fff 10%,
    #f9f9f9 15%,
    #fff 20%,
    #f9f9f9 25%,
    #fff 30%,
    #f9f9f9 35%,
    #fff 40%,
    #f9f9f9 45%,
    #fff 50%,
    #f9f9f9 55%,
    #fff 60%,
    #f9f9f9 65%,
    #fff 70%,
    #f9f9f9 75%,
    #fff 80%,
    #f9f9f9 85%,
    #fff 90%,
    #f9f9f9 95%,
    #fff 100%
    );
}

.book::after {
  position: absolute;
  top: 0;
  left: 0;
  content: ' ';
  width: var(--book-width);
  height: var(--book-height);
  transform: translateZ(calc(var(--book-spine-width) / -2));
  background-color: #01060f;
  border-radius: 0 0px 0px 0;
}