<!DOCTYPE html>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<link rel="author" title="Emilio Cobos Álvarez" href="mailto:emilio@crisal.io">
<link rel="author" title="Mozilla" href="https://mozilla.org">
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1559627">
<link rel="help" href="https://drafts.csswg.org/css-scroll-anchoring/#suppression-triggers">
<style>
  body, h1 {
    margin: 0
  }
  .sticky {
    width: 100%;
    top: 0;
    left: 0;
  }
  .sticky > div {
    width: 100%;
    height: 50px;
    background: darkblue;
  }
  header {
    background: lightblue;
  }
  main {
    background: lightgrey;
    height: 200vh;
  }
</style>
<header>
  <h1>Some title</h1>
  <span class="sticky"><div>Sticky header</div></span>
</header>
<main>
  Some actual content.
</main>
<script>
const sticky = document.querySelector(".sticky");
const nonStickyOffset = sticky.firstElementChild.offsetTop;
const t = async_test("Scroll offset adjustments are correctly suppressed when changing the position of an inline");
let firstEvent = true;
window.onscroll = t.step_func(function() {
  sticky.style.position =
    document.documentElement.scrollTop > nonStickyOffset ?  "fixed" : "static";
  if (firstEvent) {
    firstEvent = false;
    requestAnimationFrame(t.step_func(function() {
      requestAnimationFrame(t.step_func_done(function() {
        assert_equals(sticky.style.position, "fixed", "Element should become and remain fixed")
      }));
    }));
  }
});
window.onload = t.step_func(function() {
  window.scrollTo(0, nonStickyOffset + 1);
});
</script>
