.book,
.book__pg-shadow,
.book__pg {
  animation: cover 5s ease-in-out infinite;
}
.book {
  background-color: hsl(268, 90%, 65%);
  border-radius: 0.25em;
  box-shadow:
    0 0.25em 0.5em hsla(0, 0%, 0%, 0.3),
    0 0 0 0.25em hsl(278, 100%, 57%) inset;
  padding: 0.25em;
  perspective: 37.5em;
  position: relative;
  width: 8em;
  height: 6em;
  transform: translate3d(0, 0, 0);
  transform-style: preserve-3d;
}
.book__pg-shadow,
.book__pg {
  position: absolute;
  left: 0.25em;
  width: calc(50% - 0.25em);
}
.book__pg-shadow {
  animation-name: shadow;
  background-image: linear-gradient(
    -45deg,
    hsla(0, 0%, 0%, 0) 50%,
    hsla(0, 0%, 0%, 0.3) 50%
  );
  filter: blur(0.25em);
  top: calc(100% - 0.25em);
  height: 3.75em;
  transform: scaleY(0);
  transform-origin: 100% 0%;
}
.book__pg {
  animation-name: pg1;
  background-color: hsl(223, 10%, 100%);
  background-image: linear-gradient(
    90deg,
    hsla(223, 10%, 90%, 0) 87.5%,
    hsl(223, 10%, 90%)
  );
  height: calc(100% - 0.5em);
  transform-origin: 100% 50%;
}
.book__pg--2,
.book__pg--3,
.book__pg--4 {
  background-image: repeating-linear-gradient(
      hsl(223, 10%, 10%) 0 0.125em,
      hsla(223, 10%, 10%, 0) 0.125em 0.5em
    ),
    linear-gradient(90deg, hsla(223, 10%, 90%, 0) 87.5%, hsl(223, 10%, 90%));
  background-repeat: no-repeat;
  background-position: center;
  background-size:
    2.5em 4.125em,
    100% 100%;
}
.book__pg--2 {
  animation-name: pg2;
}
.book__pg--3 {
  animation-name: pg3;
}
.book__pg--4 {
  animation-name: pg4;
}
.book__pg--5 {
  animation-name: pg5;
}

/* Dark theme */
@media (prefers-color-scheme: dark) {
  :root {
    --bg: hsl(223, 10%, 30%);
    --fg: hsl(223, 10%, 90%);
  }
}

/* Animations */
@keyframes cover {
  from,
  5%,
  45%,
  55%,
  95%,
  to {
    animation-timing-function: ease-out;
    background-color: hsl(278, 84%, 67%);
  }
  10%,
  40%,
  60%,
  90% {
    animation-timing-function: ease-in;
    background-color: hsl(271, 90%, 45%);
  }
}
@keyframes shadow {
  from,
  10.01%,
  20.01%,
  30.01%,
  40.01% {
    animation-timing-function: ease-in;
    transform: translate3d(0, 0, 1px) scaleY(0) rotateY(0);
  }
  5%,
  15%,
  25%,
  35%,
  45%,
  55%,
  65%,
  75%,
  85%,
  95% {
    animation-timing-function: ease-out;
    transform: translate3d(0, 0, 1px) scaleY(0.2) rotateY(90deg);
  }
  10%,
  20%,
  30%,
  40%,
  50%,
  to {
    animation-timing-function: ease-out;
    transform: translate3d(0, 0, 1px) scaleY(0) rotateY(180deg);
  }
  50.01%,
  60.01%,
  70.01%,
  80.01%,
  90.01% {
    animation-timing-function: ease-in;
    transform: translate3d(0, 0, 1px) scaleY(0) rotateY(180deg);
  }
  60%,
  70%,
  80%,
  90%,
  to {
    animation-timing-function: ease-out;
    transform: translate3d(0, 0, 1px) scaleY(0) rotateY(0);
  }
}
@keyframes pg1 {
  from,
  to {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.4deg);
  }
  10%,
  15% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(180deg);
  }
  20%,
  80% {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(180deg);
  }
  85%,
  90% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(180deg);
  }
}
@keyframes pg2 {
  from,
  to {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(0.3deg);
  }
  5%,
  10% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.3deg);
  }
  20%,
  25% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.9deg);
  }
  30%,
  70% {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(179.9deg);
  }
  75%,
  80% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.9deg);
  }
  90%,
  95% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.3deg);
  }
}
@keyframes pg3 {
  from,
  10%,
  90%,
  to {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(0.2deg);
  }
  15%,
  20% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.2deg);
  }
  30%,
  35% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.8deg);
  }
  40%,
  60% {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(179.8deg);
  }
  65%,
  70% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.8deg);
  }
  80%,
  85% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.2deg);
  }
}
@keyframes pg4 {
  from,
  20%,
  80%,
  to {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(0.1deg);
  }
  25%,
  30% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.1deg);
  }
  40%,
  45% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.7deg);
  }
  50% {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(179.7deg);
  }
  55%,
  60% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.7deg);
  }
  70%,
  75% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0.1deg);
  }
}
@keyframes pg5 {
  from,
  30%,
  70%,
  to {
    animation-timing-function: ease-in;
    background-color: hsl(223, 10%, 45%);
    transform: translate3d(0, 0, 1px) rotateY(0);
  }
  35%,
  40% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0deg);
  }
  50% {
    animation-timing-function: ease-in-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(179.6deg);
  }
  60%,
  65% {
    animation-timing-function: ease-out;
    background-color: hsl(223, 10%, 100%);
    transform: translate3d(0, 0, 1px) rotateY(0);
  }
}