css/css-properties-values-api/at-property-shadow.html

<!DOCTYPE html>
<link rel="help" href="https://drafts.css-houdini.org/css-properties-values-api-1/#at-property-rule">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/utils.js"></script>
<style>
  @property --x {
    syntax: "<length>";
    inherits: false;
    initial-value: 0px;
  }
  #outside {
    --x: calc(1px + 1px);
    --y: calc(1px + 1px);
  }
</style>
<template id=template>
  <style>
    /* This rule should have no effect */
    @property --y {
      syntax: "<length>";
      inherits: false;
      initial-value: 0px;
    }
    #inside {
      --x: calc(1px + 1px);
      --y: calc(1px + 1px);
    }
  </style>
  <div id=inside></div>
</template>
<div id=host></div>
<div id=outside></div>
<script>

test(() => {
  let root = host.attachShadow({ mode: 'open' });
  root.append(template.content.cloneNode(true));
  let inside = root.querySelector('#inside');
  assert_equals(getComputedStyle(outside).getPropertyValue('--x'), '2px');
  assert_equals(getComputedStyle(outside).getPropertyValue('--y'), ' calc(1px + 1px)');
  assert_equals(getComputedStyle(inside).getPropertyValue('--x'), '2px');
  assert_equals(getComputedStyle(inside).getPropertyValue('--y'), ' calc(1px + 1px)');
}, '@property rules in shadow trees should have no effect');

</script>