css/css-pseudo/highlight-cascade-003.html

<!DOCTYPE html>
<title>Initial custom property values in :root::selection rule</title>
<link rel="help" href="https://drafts.csswg.org/css-pseudo-4/#highlight-cascade">
<link rel="match" href="highlight-cascade-003-ref.html">
<meta name="assert" value="This test verifies that the initial value given in a custom property registration is respected, when the property is referenced in ::selection styles but no value is defined. The initial value is not the guaranteed-invalid value, so the fallback value in var() is not used.">
<script src="support/selections.js"></script>
<style>
  @property --bg {
    syntax: "<color>";
    inherits: false;
    initial-value: green;
  }
  :root::selection {
    background-color: var(--bg, red);
  }
</style>
<main>PASS if background-color is green when selected</main>
<script>
  selectNodeContents(document.querySelector("main"));
</script>