The :before and :after pseudo-elements interact with other boxes as if they were real elements inserted just inside their associated element.

Where Firefox put the ::after ? Inside.
Where Chrome put the ::after ? After.

The problem: Chrome based on Webkit (used by nearly every navigators such as Opera, Vilvaldi, Edge) does not have to respect the standards. And Chrome doesn't.

We must follow because webkit-based webbrowsers are used by a majority of users.