In T252430#6127462, @Demian wrote:

@alexhollender margin: 0 auto; is sufficient for horizontal centering in both evergreen and old browsers, whether flexbox is supported or not, as I've written before.
While the flexbox and align rules on the parent (-container) make the intent more explicit, those only add complication and extra rules without practical benefit.
I note that I've asked to add the necessary rule a few times (phab, 1, 2, 3, 4, etc.)

What is the expected behaviour if the tagline is wider than the wordmark? Assuming the horizontal centering is expected in that case too, the .mw-logo-wordmark class needs a margin: 0 auto; rule as well.

Thanks for raising this question. I think part of the complexity here is that there is no official version of the logo+wordmark+tagline aside from the usage on the site. Since currently in Vector all taglines are centered underneath the wordmark, regardless of length, I think it's a sensible starting point. It would make sense for us to take a step back at some point, and evaluate the identity system (i.e. logo+wordmark+tagline) and figure out if we want part of the system to be that when the tagline is longer than the wordmark we left-align them. But that feels a bigger decision than I'd like to take on right now. So we'll stick with the status quo, as determined by the current version of Vector.

@Volker_E, is this intended to be tested in Beta?

Re-assigning to you @Edtadros. Think we can move it to QA in Prod after next week's train, or still opt for sign-off.