Standards have changed. For example, CSS :first-child without a parent is now legal: https://developer.mozilla.org/en-US/docs/Web/CSS/:first-child https://deve

Standards have changed. For example, CSS :first-child without a parent is now legal: https://developer.mozilla.org/en-US/docs/Web/CSS/:first-child https://developer.mozilla.org/en-US/docs/Web/CSS/:first-chil... You can shift click the "A" in Acid3 to see what's failing.