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HTML

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CSS

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JavaScript

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Babel includes JSX processing.

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HTML 

              
                <a class="btn btn-primary" href="https://www.erwinhofman.nl/blog/improve-pagespeed-with-content-visibility-css-for-you/" target="_blank">Back to the article</a>
<div class="container">
  <section>
    <p class="large">When on desktop + Chrome/Edge or Opera, try to scroll by grabbing the scrollbar without getting frustrated ;)</p>
  </section>
  <section>
    <p>Lorem ipsum dolor sit amet, consectetur adipiscing elit. Nullam faucibus blandit mollis. Integer tristique rutrum laoreet. Nulla sed varius augue, non viverra enim. Sed auctor erat eu fermentum varius. Nulla lobortis non ex et elementum. Cras eu nunc blandit, tincidunt nisl nec, facilisis mi. Donec feugiat nisi nibh, eu gravida leo sodales ac. Praesent posuere velit nec feugiat dictum. Nullam ac ligula sit amet mauris aliquet varius non quis ligula. Sed et elementum urna. Etiam fermentum sollicitudin massa, bibendum varius ex mattis eu. Etiam eu diam ut ex tempus finibus at eu turpis. In risus sem, vehicula ut justo lobortis, semper facilisis quam. Vestibulum vel cursus justo, vitae finibus dolor. Pellentesque habitant morbi tristique senectus et netus et malesuada fames ac turpis egestas.</p>
  </section>
  <section>
    <p>Nullam vel ipsum sem. Suspendisse euismod vehicula ligula, a suscipit quam malesuada eget. Vestibulum ultricies at magna quis venenatis. Sed non sem quis sem sagittis aliquet id in quam. Suspendisse tristique nibh mi, eget ullamcorper sapien finibus nec. Morbi non tempus enim. Curabitur lacinia sem ac diam vehicula, ultricies commodo dolor viverra. Vivamus commodo varius velit, sit amet auctor dui suscipit aliquam. Integer sed felis vel dui vestibulum interdum. Sed bibendum mi et quam auctor vestibulum. Integer tincidunt est elit, eu lobortis dolor rhoncus at. Aenean et ex efficitur, hendrerit dui ac, feugiat justo. Pellentesque cursus lacinia est, at ultrices sem convallis vel.</p>
  </section>
  <section>
    <p>Quisque rhoncus sapien quam, vel sodales elit sollicitudin id. Aenean iaculis justo in felis hendrerit, eget sagittis quam tristique. Fusce tempor, enim sit amet tristique gravida, velit ante lobortis erat, et volutpat purus justo sit amet metus. Nunc porta consequat pretium. Maecenas imperdiet euismod tortor, eu mollis nulla sagittis eget. Maecenas ultricies neque sit amet finibus tempor. In nec pharetra enim. Vestibulum augue mauris, facilisis eu elit ut, sollicitudin malesuada lacus. Maecenas quis tempus orci, ut posuere dui.</p>
  </section>
  <section>
    <p>Quisque ultricies maximus dapibus. Etiam egestas congue erat quis ultrices. Aenean id diam rutrum, cursus dolor eu, tempus ipsum. In ante lorem, pellentesque id sapien id, lobortis placerat orci. Integer mollis nisi dapibus eros fermentum pellentesque. Ut eget tortor sed justo cursus venenatis eu ut elit. Sed sodales dapibus leo, et vulputate massa varius nec. Morbi porttitor auctor ornare. In faucibus, dui sed ullamcorper congue, sapien mi imperdiet ante, ultrices ultrices lacus urna eu diam. Praesent sed libero eget nunc pellentesque cursus. In hac habitasse platea dictumst. Maecenas et scelerisque ex. Quisque ultricies ut nibh ut tempus. Fusce id sem mi. Integer et est in sapien bibendum pharetra. Phasellus faucibus, elit vel commodo mollis, risus dui tempus enim, at imperdiet magna turpis a odio.</p>
  </section>
  <section>
    <p>Maecenas in euismod felis. Sed at volutpat quam. Pellentesque ac libero eu justo scelerisque porttitor eu vel eros. Morbi lorem massa, commodo in ultrices in, tristique vel sem. Aliquam porttitor justo ut risus condimentum, a aliquam orci tempus. Nulla sollicitudin felis ac augue facilisis dictum. Nam tortor justo, venenatis interdum leo non, finibus accumsan ligula. In augue enim, pellentesque nec malesuada in, condimentum ac nulla.</p>
  </section>
</div>
!

CSS 

              
                body {
  margin: 2rem;
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto,
    "Helvetica Neue", Arial, sans-serif, "Apple Color Emoji", "Segoe UI Emoji",
    "Segoe UI Symbol";
}
.container {
  max-width: 500px;
}
section {
  content-visibility: auto;
}

.large {
  font-size: 1.3em;
}
a {
  position: fixed;
  top: 0;
  right: 0;
  margin: 2rem;
  z-index: 1;
}
.btn {
  display: inline-block;
  font-weight: 500;
  text-align: center;
  white-space: nowrap;
  vertical-align: middle;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  border: 1px solid transparent;
  padding: 0.75rem 1.75rem;
  font-size: 1rem;
  line-height: 1.5;
  border-radius: 0.25rem;
  background-color: transparent;
  transition: background-color 0.2s ease-in-out, border-color 0.2s ease-in-out;
}
.btn-primary {
  color: #fff;
  background-color: #008aff;
  border-color: #008aff;
  box-shadow: none;
}
!

JS
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999px

Console