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CSS

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CSS Base

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HTML 

              
                <input type="checkbox" id="pcb">
<div class="pendulum">

  <div class="topbar">
    <div></div><div></div><div></div><div></div><div></div><div></div>
  </div>

  <div class="balls">
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
    <div class="ball">
      <div class="string"></div>
      <div class="string"></div>
      <div class="face"></div>
    </div>
  </div>

  <div class="floor">
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
    <div class="shadow"></div>
  </div>
</div>

<label for="pcb">
  <svg xmlns="http://www.w3.org/2000/svg" viewBox="0 0 50 50">
    <path d="M 25 13 C 19.184825 13 13.344702 13.859292 8.8515625 15.605469 C 6.604993 16.478557 4.68813 17.572147 3.2851562 18.955078 C 1.8821826 20.338009 1 22.065021 1 24 C 1 25.765502 1.7336163 27.364275 2.9277344 28.673828 C 4.1218525 29.983381 5.7648812 31.042084 7.703125 31.912109 C 11.339472 33.544367 16.075891 34.455277 21 34.798828 L 21 41.044922 L 32.628906 32 L 21 22.955078 L 21 28.777344 C 16.699262 28.438697 13.10263 27.646111 10.683594 26.658203 C 9.3674634 26.12071 8.3719281 25.537579 7.7597656 25.021484 C 7.1476032 24.50539 7 24.096639 7 24 C 7 23.892861 7.1957082 23.405298 7.9492188 22.822266 C 8.7027293 22.239233 9.9098427 21.595327 11.490234 21.023438 C 14.651019 19.879656 19.303144 19 25 19 C 30.696856 19 35.348981 19.879656 38.509766 21.023438 C 40.090158 21.595327 41.297271 22.239233 42.050781 22.822266 C 42.804292 23.405298 43 23.892861 43 24 C 43 24.12216 42.684049 24.776886 41.615234 25.482422 C 40.546419 26.187958 38.876371 26.929655 36.728516 27.537109 L 36 27.744141 L 36 33.917969 L 37.240234 33.611328 C 40.490536 32.807479 43.346925 31.663594 45.466797 30.101562 C 47.586668 28.539531 49 26.457731 49 24 C 49 22.065021 48.117818 20.338009 46.714844 18.955078 C 45.31187 17.572147 43.395007 16.478557 41.148438 15.605469 C 36.655298 13.859292 30.815175 13 25 13 z M 25 15 C 30.614825 15 36.274467 15.85813 40.423828 17.470703 C 42.498509 18.27699 44.188911 19.273322 45.3125 20.380859 C 46.436089 21.488397 47 22.652479 47 24 C 47 25.711269 46.078379 27.166016 44.28125 28.490234 C 42.746774 29.620916 40.514291 30.536314 38 31.267578 L 38 29.154297 C 39.878459 28.560545 41.572518 27.905742 42.716797 27.150391 C 44.037732 26.278427 45 25.31184 45 24 C 45 22.884139 44.270238 22.011515 43.273438 21.240234 C 42.276636 20.468954 40.909311 19.764937 39.189453 19.142578 C 35.749737 17.89786 30.901144 17 25 17 C 19.098856 17 14.250263 17.89786 10.810547 19.142578 C 9.0906889 19.764937 7.7233644 20.468954 6.7265625 21.240234 C 5.7297606 22.011515 5 22.884139 5 24 C 5 25.016861 5.6222406 25.83547 6.4707031 26.550781 C 7.3191657 27.266093 8.4753645 27.916634 9.9277344 28.509766 C 12.832474 29.696029 16.925171 30.629986 21.945312 30.908203 L 23 30.966797 L 23 27.042969 L 29.373047 32 L 23 36.957031 L 23 32.970703 L 22.052734 32.919922 C 16.960744 32.651276 12.052997 31.673091 8.5214844 30.087891 C 6.7557282 29.295291 5.3421319 28.352525 4.40625 27.326172 C 3.4703681 26.299819 3 25.229498 3 24 C 3 22.652479 3.5639113 21.488397 4.6875 20.380859 C 5.8110887 19.273322 7.5014914 18.27699 9.5761719 17.470703 C 13.725533 15.85813 19.385175 15 25 15 z"/>
  </svg>
</label>
!

CSS 

              
                * {
  padding: 0;
  margin: 0 auto;
  box-sizing: border-box;
}

body {
  background-color: #000;
  color: #fff;
  min-height: 100vh;
  display: grid;
  place-items: center;
  font-size: 40px;
  perspective: 50em;

  *:not(:empty) {
    transform-style: preserve-3d;
  }
}

input[type="checkbox"] {
  display: none;

  &:checked ~ .pendulum {
    --ry: 360deg;
  }
  &:checked ~ label {
    --ry: 180deg;
  }
}

label {
  position: fixed;
  top: calc(50% - 7em);
  cursor: pointer;
  transform: rotateY(var(--ry, 0));
  transition: transform 5s;

  &:hover > svg {
    opacity: 0.5;
  }

  svg {
    width: 3em; height: 2em;
    fill: #fff;
    opacity: 0.3;
  }
}

.pendulum {
  position: relative;
  transform: rotateY(var(--ry, 0deg));
  transition: transform 10s;
}

.topbar {
  position: absolute;
  top: -4em;

  & > div {
    position: absolute;
    width: 1em; height: var(--height, 1em);
    background-color: #420;
    transform: translate(-50%, -50%) var(--transform, );
    box-shadow: 0 0 1em #000 inset;
    opacity: 0.9;

    &:nth-child(1) { --transform: translateZ(8em);}
    &:nth-child(2) { --transform: rotateY(180deg) translateZ(8em);}

    @for $i from 0 to 4 {
      &:nth-child(#{$i + 3}) {
        --height: 16em;
        --transform: rotateZ(#{$i * 90deg}) rotateX(90deg) translateZ(0.5em);
      }
    }
  }
}

.balls {
  position: absolute;
  top: -3.5em;
}

.ball {
  position: absolute;
  animation: ballSwing var(--duration, 0s) calc(var(--duration, 0s) * -0.5) infinite ease-in-out alternate;

  @keyframes ballSwing {
    from { transform: translateZ(var(--tz, 0)) rotateZ(-45deg); }
    to { transform: translateZ(var(--tz, 0)) rotateZ(45deg); }
  }

  .string {
    position: absolute;
    left: -1px;;
    width: 2px; height: calc(var(--ty, 0) - 0.5em);
    background-color: hsla(var(--hue, 0), 75%, 75%, 0.1);
    transform: rotateX(var(--rx, -3deg));
    transform-origin: bottom;
    transform-style: preserve-3d;

    &:nth-child(2) { --rx: 3deg; }

    &::before, &::after {
      content: '';
      position: absolute;
      inset: 0;
      transform: rotateY(var(--ry, 120deg));
      background-color: inherit;
    }

    &::after { --ry: 240deg; }
  }

  & .face {
    position: absolute;
    animation: faceSwing var(--duration, 0s) calc(var(--duration, 0s) * -0.5) infinite ease-in-out alternate-reverse;
    transform-style: preserve-3d;

    @keyframes faceSwing {
      from { transform: translateY(var(--ty, 5em)) rotateZ(-45deg); }
      to { transform: translateY(var(--ty, 5em)) rotateZ(45deg); }
    }

    &::after {
      content: '';
      position: absolute;
      width: 1em; height: 1em;
      background-color: hsl(var(--hue, 0), 75%, 75%);
      background-image: radial-gradient(circle at top, #0000, #000);
      border-radius: 50%;
      box-shadow: 0 0 1em #000;
      transform: translate(-50%, -50%) rotateY(var(--ry, 720deg));
      transition: transform 10s;
    }
  }
}

.floor {
  position: absolute;
  top: 7em;
  width: 30em; height: 30em;
  background-color: #024;
  background-image: 
    radial-gradient(#0000, #000 15em),
    repeating-conic-gradient(from 20deg, #000 0 90deg, #0000 0 180deg);
  background-size: 100% 100%, 2em 2em;
  transform: translate(-50%, -50%) rotateX(90deg);
}

.shadow {
  position: absolute;
  left: 50%; top: calc(50% + var(--tz, 0em));
  width: calc(6em - var(--ty, 0) * 0.2); height: calc(8em - var(--ty, 0) * 0.2);
  border-radius: 50%;
  background-image: radial-gradient(#000, #0000 50%);
  animation: shadow var(--duration) calc(var(--duration, 0s) * -0.5) infinite ease-in-out alternate;
  transform: translate(-50%, -50%);

  @keyframes shadow {
    from { transform: translate(-50%, -50%) translateX(10em); }
    to { transform: translate(-50%, -50%) translateX(-10em); }

    0%, 100% { opacity: 0; }
    50% { opacity: 1; }
  }
}

.ball, .shadow {
  @for $i from 0 to 15 {
    &:nth-child(#{$i + 1}) {
      --tz: #{$i - 7}em;
      --duration: #{30 / (30 - $i)}s; // #{math.div(36, 30 - $i)}s;
      --ty: #{6 + $i * 0.25}em;
      --hue: #{$i * 24};
    }
  }
}
!

JS
!
999px

Console