chromium/third_party/blink/web_tests/external/wpt/focus/scroll-matches-focus.html

<!doctype html>
<meta charset=utf-8>
<title>:focus applies before scrolling into view</title>
<link rel="help" href="https://bugzilla.mozilla.org/show_bug.cgi?id=1775451">
<link href="mailto:[email protected]" title="Emilio Cobos Álvarez">
<link href="https://mozilla.com" title="Mozilla">
<script src=/resources/testharness.js></script>
<script src=/resources/testharnessreport.js></script>
<style>
body {
  margin: 0;
}
.padding {
  height: 200vh;
  background-color: purple;
}
#focusable {
  z-index: 0;
  position: absolute;
  top: 0;
  left: 0;
}
#focusable:focus {
  z-index: 1;
  left: auto;
  top: auto;
}
</style>
<div class="padding"></div>
<div id="focusable" tabindex=0>I am focusable</div>
<div class="padding"></div>
<script>
onload = function() {
  async_test(function(t) {
    let focusable = document.getElementById("focusable");
    assert_equals(getComputedStyle(focusable).zIndex, "0", "focusable style is correct");

    window.addEventListener("scroll", t.step_func_done(function(e) {
      assert_equals(document.activeElement, focusable, "activeElement should be set");
      assert_true(focusable.matches(":focus"), ":focus should match by the time we scroll");
      assert_equals(getComputedStyle(focusable).zIndex, "1", "focusable style is correct");
    }), { once: true });

    focusable.focus();
  });
};
</script>