<!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>