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HTML 

              
                <nav class="shelf">
  <a class="book home-page">Home page</a>
  <a class="book about-us">About us</a>
  <a class="book contact">Contact</a>
  <a class="book faq">F.A.Q.</a>
  
  <span class="book not-found"></span>
 
  <span class="door left"></span>
  <span class="door right"></span>
</nav>
<h1>Error 404</h1>
<p>The page you're loking for can't be found</p>
!

CSS 

              
                @import url(https://fonts.googleapis.com/css?family=Dancing+Script:400,700);
@use postcss-nested;

body, html {
  height: 100%;
}

body {
  margin: 0;
  padding: 2rem;
  background-color: #446072;
  font-family: monospace;
  color: white;
  overflow: hidden;
}
h1 {
  margin-top: 2rem;
  text-align: center;
}
h1 + p {
  text-align: center;
}
.shelf {
  position: relative;
  width: 30rem;
  height: 14rem;
  margin: 0 auto;
  border: 0.5rem solid #374d5b;
  border-radius: 0.5rem;
  background-color: rgba(255, 255, 255, 0.1);
  perspective: 130rem;
  box-shadow: inset 0 0 2rem rgba(0, 0, 0, 0.2);
}
.door {
  position: absolute;
  width: 14.8rem;
  height: 14rem;
  display: flex;
  box-sizing: border-box;
  padding: 1rem;
  background-color: #374d5b;
  align-items: center;
  box-shadow: 0 1px 1px rgba(0, 0, 0, 0.3);
  outline: 1px solid transparent;
  &::before {
    width: 1.5rem;
    height: 1.5rem;
    border-radius: 50%;
    background-color: rgba(0, 0, 0, 0.1);
    content: "";
  }
  &.left {
    border-radius: 0 0.75rem 0.75rem 0;
    justify-content: flex-end;
    animation: 
      leftDoorOpen 3.5s ease-out forwards 1s,
      leftDoorFlap 15s linear infinite forwards 9s;
    transform-origin: 0 0 0;
  }
  &.right {
    right: 0;
    border-radius: 0.75rem 0 0 0.75rem;
    animation: 
      rightDoorOpen 3s ease-out forwards 1.5s,
      rightDoorFlap 10s linear infinite forwards 8s;
    transform-origin: 100% 0 0;
  }
}
.book {
  position: absolute;
  box-sizing: border-box;
  padding: 0.8rem 4rem 0.8rem 2rem;
  border-radius: 0.25rem;
  background-color: rgba(255, 255, 255, 0.1);
  color: white;
  font-size: 1rem;
  text-transform: uppercase;
  letter-spacing: 0.1rem;
  cursor: pointer;
  box-shadow: inset 0 0 0.75rem rgba(255, 255, 255, 0.1);
  &.home-page {
    transform: rotate(-90deg) translate(-12.4rem, 3rem);
    transform-origin: 0;
  }
  &.about-us {
    transform: rotate(-100deg) translate(-13.4rem, 6.1rem);
    transform-origin: 0;
    outline: 1px solid transparent;
  }
  &.contact {
    right: 2rem;
    bottom: 0.2rem;
    border-radius: 0.3rem 0 0 0.3rem;
  }
   &.faq {
    right: 0.8rem;
    bottom: 3.3rem;
    border-radius: 0.3rem 0 0 0.3rem;
  }
  &.not-found {
    width: 12rem;
    height: 3.5rem;
    border: 1px dashed rgba(255, 255, 255, 0.3);
    background-color: transparent;
    transform: rotate(-90deg) translate(-12rem, 13rem) scale(1);
    transform-origin: 0;
    cursor: default;
    animation: bookFadeOut 1s 3s infinite forwards;
    
    &::after {
      display: block;
      width: 10rem;
      padding-left: 5rem;
      background-image: url("data:image/svg+xml;utf8,<svg xmlns='http://www.w3.org/2000/svg' width='80' height='30'><path fill='rgb(255, 255, 255)' d='M7.688,3.737C6.1,10.409,4.624,16.982,2.475,23.517c-0.424,1.29,0.724,2.338,1.957,1.916 c5.879-2.021,11.743-4.107,17.409-6.696c1.246-0.572,0.443-2.366-0.815-1.932c-3.856,1.333-7.695,2.69-11.565,3.959 c2.879-2.526,5.485-5.215,9.013-7.17c4.441-2.459,9.299-4.109,14.281-4.915c10.903-1.772,22.052,0.562,31.979,5.04 c9.241,4.162,12.895,8.725,13.164,4.942c0.121-1.69-5.57-4.953-14.125-8.714C53.19,5.292,41.094,3.539,29.636,6.058 c-7.122,1.567-16.708,5.374-22.064,11.544c1.359-4.455,2.461-9.028,3.032-13.563C10.852,2.091,8.12,1.927,7.688,3.737z'/></svg>");
      background-repeat: no-repeat;
      background-size: 4rem;
      background-position: left center;
      font-family: "Dancing Script";
      text-transform: lowercase;
      font-size: 25px;
      content: "this page can't be found";
      transform: rotate(90deg) translate(6rem, -1rem);
      opacity: 0.3; 
    }
  }
  &:hover:not(.not-found) {
    background-color: rgba(255, 255, 255, 0.2);
  }
}
@keyframes leftDoorOpen {
  60% {transform: rotateY(-115deg)}
  100% {transform: rotateY(-110deg)}
}
@keyframes rightDoorOpen {
  60% {transform: rotateY(125deg)}
  100% {transform: rotateY(120deg)}
}
@keyframes rightDoorFlap {
  0% { transform: rotateY(120deg)}
  5% {transform: rotateY(125deg)}
  15% {transform: rotateY(117deg)}
  25% {transform: rotateY(123deg)}
  30% {transform: rotateY(120deg)}
  100% {transform: rotateY(120deg)}
}
@keyframes leftDoorFlap {
  0% { transform: rotateY(-110deg)}
  5% {transform: rotateY(-115deg)}
  15% {transform: rotateY(-107deg)}
  25% {transform: rotateY(-113deg)}
  30% {transform: rotateY(-110deg)}
  100% {transform: rotateY(-110deg)}
}
@keyframes bookFadeOut {
  50% {border: 1px dashed rgba(255, 255, 255, 0.1);}
}
!

JS
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