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HTML

              
                <header id="page-header">
  <div class="site-name">📜 Shadow Scrolls</div>
  <nav>
    <ul class="menu" role="list">
      <li><a href="#">Shop</a></li>
      <li><a href="#">Blog</a></li>
      <li><a href="#">About</a></li>
      <li><a href="#">Contact</a></li>
    </ul>
  </nav>
</header>
<main>
  <div class="warning">
    <p>⚠️ Scroll-driven animations are not supported in this browser. Try this demo in Chrome 115+.</p>
  </div>
  <p>Scroll down 👇</p>
</main>
              
            
!

CSS

              
                header {
  --shadow: hsla(0 0% 0% / 0.1) 0 0.5rem 1rem;
  position: sticky;
  top: 0;
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 1rem;
  padding: 2rem clamp(1rem, 4vw, 2rem);
  background-color: white;

  /* Fall back to persistent shadow */
  box-shadow: var(--shadow);
}

/* Fade in shadow on scroll when supported */
@supports (animation-timeline: scroll()) {
  header {
    animation: scroll-shadow linear both;
    animation-timeline: scroll();
    animation-range: 0ex 5ex;
  }

  @keyframes scroll-shadow {
    from {
      box-shadow: none;
    }

    to {
      box-shadow: var(--shadow);
    }
  }
}

/* Other demo styles */

.site-name {
  font-weight: bold;
}

.menu {
  display: flex;
  gap: 1rem;
}

.menu a {
  color: inherit;
  text-decoration: none;
}

main {
  height: 300vh;
  margin-block-start: 5rem;
  text-align: center;
}

body {
  font-family: system-ui, sans-serif;

  /* Easing gradient: https://larsenwork.com/easing-gradients/ */
  background: linear-gradient(
    to bottom,
    hsl(0, 0%, 100%) 0%,
    hsl(219.19, 55.23%, 99.76%) 10.6%,
    hsl(219.13, 55.37%, 99.05%) 20%,
    hsl(219.05, 55.59%, 97.92%) 28.4%,
    hsl(218.92, 55.89%, 96.39%) 35.8%,
    hsl(218.76, 56.28%, 94.49%) 42.6%,
    hsl(218.55, 56.76%, 92.22%) 48.7%,
    hsl(218.29, 57.33%, 89.61%) 54.4%,
    hsl(217.96, 58%, 86.67%) 59.8%,
    hsl(217.56, 58.78%, 83.39%) 64.9%,
    hsl(217.06, 59.69%, 79.76%) 70.1%,
    hsl(216.42, 60.75%, 75.77%) 75.3%,
    hsl(215.6, 62%, 71.35%) 80.8%,
    hsl(214.5, 63.51%, 66.41%) 86.6%,
    hsl(212.9, 65.42%, 60.66%) 93%,
    hsl(210.18, 68.2%, 53.14%) 100%
  );
}

/* Warning for unsupported browsers */
.warning {
  color: black;
  background: papayawhip;
  margin: 1rem auto;
  padding: 1rem;
  max-width: fit-content;
}

@supports (animation-timeline: scroll()) {
  .warning {
    display: none;
  }
}

              
            
!

JS

              
                /** 
Updated demo using CSS scroll-driven animations instead of the Intersection Observer API. Created for the "Sticky Page Header Shadow on Scroll" article: https://ryanmulligan.dev/blog/sticky-header-scroll-shadow/
*/

              
            
!
999px

Console