Title attribute should be ignored for style elements in shadow trees. On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE". PASS getComputedStyle(root.querySelector('div')).color is "rgb(0, 128, 0)" PASS getComputedStyle(alternate).color is "rgb(0, 128, 0)" PASS host.shadowRoot.styleSheets[0].title is null PASS successfullyParsed is true TEST COMPLETE Should be green