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HTML

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About the <head>

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CSS

About CSS Preprocessors

CSS preprocessors help make authoring CSS easier. All of them offer things like variables and mixins to provide convenient abstractions.

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CSS Base

About CSS Base

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About Vendor Prefixing

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JavaScript

About JavaScript Preprocessors

JavaScript preprocessors can help make authoring JavaScript easier and more convenient.

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Babel includes JSX processing.

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Packages

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Search for and use JavaScript packages from npm here. By selecting a package, an import statement will be added to the top of the JavaScript editor for this package.

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HTML 

              
                <main>
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
  <div>5</div>
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
  <div>5</div>
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
  <div>5</div>
  <div>1</div>
  <div>2</div>
  <div>3</div>
  <div>4</div>
  <div>5</div>
  <div class="cover"></div>
</main>
<button id="go">Play/Pause</button>
!

CSS 

              
                :root {
  --pixel: 5vw;
  --cover: black;
  --duration: 2500ms;
  --covered: calc(var(--pixel) * 5); /*5 frames, 4 covered at a time */
  --space: white; /* will cause transparency when mix blend mode multiply */
  --w: 100vw;
  --h: calc(100vh - 3rem);
  
  --direction: normal;
  --blend: multiply;
}
main div {
  width: var(--pixel);
  
  background-image: linear-gradient(to bottom, hsl(var(--hue, 183), 100%, 52%) 80%, transparent 80%);
  
  display: flex;
  justify-content: center;
  align-items: flex-end;
  padding-bottom: .5rem;
  color: #373737;
}

main div:nth-of-type(5n + 2) {
  --hue: 255;
}
main div:nth-of-type(5n + 3) {
  --hue: 327;
}
main div:nth-of-type(5n + 4) {
  --hue: 39;
}
main div:nth-of-type(5n + 5) {
  --hue: 111;
}

.no-animation {
  --show: paused;
}


/*the sliding cover that triggers the motion illusion */
.cover {
  left: -25vw;
  width: 150vw;
  background: 
    linear-gradient(to right, 
      transparent 0px, transparent 20%, 
      var(--cover) 20%, 
      var(--cover) 100%);
  background-size: 25vw 100%;
  will-change: transform;
  transform: translateY(-50%) translateX(0px);
  
  animation: slide var(--duration) infinite var(--direction) steps(5);
  animation-play-state: var(--show, running);
  position: absolute;
  top: 0;
  bottom: 0;
}

@keyframes slide {
  100% {
    transform: translateY(-50%) translateX(var(--covered));
  }
}


main {
  width: var(--w);
  height: var(--h);
  position: relative;
  overflow: hidden;
  display: flex;
}
*, *::after {
  box-sizing: border-box;
}










body {
  width: 100%;
  min-height: 100vh;
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  background: hsl(203, 50%, 98%);
  margin: 0;
  overflow: hidden;
  overflow-y: scroll;
  
  font-family: system-ui, 'Segoe UI', sans-serif
}

button {
  appearance: none;
  background: transparent;
  border: .1rem solid currentColor;
  margin-top:.5rem;
  padding: .5rem 1rem;
  font-size: 1rem;
  background: hsl(203, 50%, 94%);
}
!

JS 

              
                document.getElementById('go').addEventListener('click', function() {
  document.documentElement.classList.toggle('no-animation');
})
!
999px

Console