transition.ready.then(() => {
      let style = getComputedStyle(document.documentElement, "::view-transition-group(root)");
      if (style.backgroundColor == "rgb(255, 0, 0)" && style.color == "rgb(255, 0, 0)")
        resolve();
      else
        reject(style.backgroundColor + " and " + style.color);
    });
  });
}, ":only-child should match because ::view-transition-group is generated for root element only");

promise_test((t) => {
  assert_implements(document.startViewTransition, "Missing document.st