<div class="book">
  <div class="book__pg-shadow"></div>
  <div class="book__pg"></div>
  <div class="book__pg book__pg--2"></div>
  <div class="book__pg book__pg--3"></div>
  <div class="book__pg book__pg--4"></div>
  <div class="book__pg book__pg--5"></div>
</div>

* {
  border: 0;
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
:root {
  --hue: 223;
  --bg: hsl(var(--hue),10%,90%);
  --fg: hsl(var(--hue),10%,10%);
  --primary: hsl(var(--hue),90%,55%);
  --primary-l: hsl(var(--hue),90%,65%);
  --primary-d: hsl(var(--hue),90%,45%);
  --white: hsl(var(--hue),10%,100%);
  --white-d: hsl(var(--hue),10%,45%);
  font-size: calc(16px + (24 - 16) * (100vw - 320px) / (1280 - 320));
}
body {
  background-color: var(--bg);
  color: var(--fg);
  font: 1em/1.5 sans-serif;
  height: 100vh;
  display: grid;
  place-items: center;
}
.book,
.book__pg-shadow,
.book__pg {
  animation: cover 7s ease-in-out infinite;
}
.book {
  background-color: var(--primary-l);
  border-radius: 0.25em;
  box-shadow:
    0 0.25em 0.5em hsla(0,0%,0%,0.3),
    0 0 0 0.25em var(--primary) 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: var(--white);
  background-image: linear-gradient(90deg,hsla(var(--hue),10%,90%,0) 87.5%,hsl(var(--hue),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(var(--hue),10%,10%) 0 0.125em,hsla(var(--hue),10%,10%,0) 0.125em 0.5em),
    linear-gradient(90deg,hsla(var(--hue),10%,90%,0) 87.5%,hsl(var(--hue),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(var(--hue),10%,30%);
    --fg: hsl(var(--hue),10%,90%);
  }
}

/* Animations */
@keyframes cover {
  from, 5%, 45%, 55%, 95%, to {
    animation-timing-function: ease-out;
    background-color: var(--primary-l);
  }
  10%, 40%, 60%, 90% {
    animation-timing-function: ease-in;
    background-color: var(--primary-d);
  }
}
@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: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.4deg);
  }
  10%, 15% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(180deg);
  }
  20%, 80% {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(180deg);
  }
  85%, 90% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(180deg);
  }
}
@keyframes pg2 {
  from, to {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(0.3deg);
  }
  5%, 10% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.3deg);
  }
  20%, 25% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.9deg);
  }
  30%, 70% {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(179.9deg);
  }
  75%, 80% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.9deg);
  }
  90%, 95% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.3deg);
  }
}
@keyframes pg3 {
  from, 10%, 90%, to {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(0.2deg);
  }
  15%, 20% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.2deg);
  }
  30%, 35% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.8deg);
  }
  40%, 60% {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(179.8deg);
  }
  65%, 70% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.8deg);
  }
  80%, 85% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.2deg);
  }
}
@keyframes pg4 {
  from, 20%, 80%, to {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(0.1deg);
  }
  25%, 30% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.1deg);
  }
  40%, 45% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.7deg);
  }
  50% {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(179.7deg);
  }
  55%, 60% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.7deg);
  }
  70%, 75% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0.1deg);
  }
}
@keyframes pg5 {
  from, 30%, 70%, to {
    animation-timing-function: ease-in;
    background-color: var(--white-d);
    transform: translate3d(0,0,1px) rotateY(0);
  }
  35%, 40% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0deg);
  }
  50% {
    animation-timing-function: ease-in-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(179.6deg);
  }
  60%, 65% {
    animation-timing-function: ease-out;
    background-color: var(--white);
    transform: translate3d(0,0,1px) rotateY(0);
  }
}