Today I learned

Hightlight text on scroll

Scroll-driven animations are a new technqiue coming to CSS that I'm the most excited about in years. It allows you to animate elements based on the scroll position of the page.

The best thing about this is, that it's a new set of APIs that work with the existing Web Animations API and CSS Animations API.

Most features of it are only available in Chrome so far but I'm sure other browsers will follow soon.

I'm collecting all the resources I can find about scroll-driven animations and plan to share a huge blog post about it on how to use them as soon as we have major browser support.

In a recent blog post, Chris Coyier shares a great way to make use of this new technqiue to highlight text on scroll ↗ Opens in new tab.

He uses the mark element to highlight text and then animates the background-size of it.

<p>
  <mark class="scroll-highlight">Scroll-driven animations</mark> are a new
  technqiue coming to CSS that I'm the most excited about in years. It allows
  you to animate elements based on the scroll position of the page.
</p>

mark.scroll-highlight {
  background-size: 100% 100%;
  background-repeat: no-repeat;
  background-color: transparent;
  background-image: linear-gradient(purple, purple);

  @supports (animation-timeline: view()) {
    animation: mark-it linear;
    animation-fill-mode: forwards;
    animation-timeline: view();
    animation-iteration-count: 1;
    animation-range: contain 0% contain 25%;
  }
}

@keyframes mark-it {
  0% {
    background-size: 0 100%;
  }
  100% {
    background-size: 100% 100%;
  }
}

With this CSS he animates the background-size of the mark element from 0% 100% to 100% 100% when it's in the viewport. The animation-range property is responsible for that and starts the animation as soon as the element is fully in the viewport and finishes it when it's 25% of the way up the currently viewport.

Here is a Demo of it on CodePen - Home Scroll Timeline <mark> Element ↗ Opens in new tab.

This looks awesome and I can't wait to use it on my own site!

I hope you enjoyed this post and learned something new. If you have any questions, feel free to reach out to me on Twitter ↗ Opens in new tab or via Email ↗ Opens in new tab.

If you want to support me, you can buy me a coffee. I would be very happy about it!

I wish you a wonderful day! Marco