If this is approved by the performance team I'm happy to send a patch to implement it myself

Related work recently:

• Rename mediawiki.special.userlogin.signup.js to mediawiki.special.createaccount (change 598217).
• mediawiki.special.userlogin.signup: Remove unused debounce dependency (change 535761) , ref T213426.
• Merge htmlform.checker.js into special.userlogin.signup.js module (change 597903), ref T253362.

Related work that is unfinished, that may serve as a first step to untangle some of this:

• Clean up old/confusing module structure (change 598216)

Before continuing, it may help to first figure out who would own/test/verify this.

Change 723634 had a related patch set uploaded (by DannyS712; author: DannyS712):

[mediawiki/core@master] Merge mediawiki.special.userlogin.(common|login|signup).styles

https://gerrit.wikimedia.org/r/723634

Tagging Growth-Team for opinion on the visual change that this is likely to make to the Create Account page on mobile.

I simulated the change as follows:

• Open https://en.m.wikipedia.org/w/index.php?title=Special:CreateAccount&debug=true and https://en.wikipedia.org/w/index.php?title=Special:CreateAccount&debug=true.
• Open DevTools on Network, filtered on CSS, and locate the mediawiki.special.userlogin.signup.styles response in the second tab, and copy its contents to the end of the "mediawiki.special.userlogin.common.styles" entry in the first tab under "Style Editor".

Currently	Changed

I suspect that the absence of this is historically not intentional but by accident given that the "login" equivalent of these are already loaded on mobile, and the way some (but not all) of the fields are currently unlimited in width seems an unlikely design choice.

Moving to Needs Discussion for us to discuss the UI changes this would entail + code review

This is how I see those pages:

login	signup

so pretty much identical, and non-full-width above ~1000px viewport width. If the patch changes that, that would be a bug.
(Adding Reading Web as they maintain the mobile skin of these pages.)

In T286842#7407111, @Tgr wrote:

This is how I see those pages:

login	signup

so pretty much identical, and non-full-width above ~1000px viewport width. If the patch changes that, that would be a bug.
(Adding Reading Web as they maintain the mobile skin of these pages.)

My screenshots:

1. patch

2. no patch

The patch version seems problematic.

Also, at a wider viewport, the line height seems wrong:

1. patch

2. no patch

The login screen seems off as well on wider viewport:

1. patch

2. no patch

On a phone sized viewport it seems less wrong, but notable that "Join {SITENAME}" is pushed down to the bottom of the viewport, presumably out of the viewport in smaller displays:

1. patch

2. no patch

cc @RHo @MMiller_WMF

In T286842#7407578, @kostajh wrote:

In T286842#7407111, @Tgr wrote:

This is how I see those pages:

login	signup

so pretty much identical, and non-full-width above ~1000px viewport width. If the patch changes that, that would be a bug.
(Adding Reading Web as they maintain the mobile skin of these pages.)

My screenshots:

1. patch

2. no patch

The patch version seems problematic.

Also, at a wider viewport, the line height seems wrong:

1. patch

2. no patch

The login screen seems off as well on wider viewport:

1. patch

2. no patch

On a phone sized viewport it seems less wrong, but notable that "Join {SITENAME}" is pushed down to the bottom of the viewport, presumably out of the viewport in smaller displays:

1. patch

2. no patch

cc @RHo @MMiller_WMF

I agree the patch appears to be introducing a pretty noticeable display bug in making the fields non-full width on devices (most noticeable on @kostajh's screenshot F34677048).
Since Reading Web maintains the mobile skin though, would this be handled on their backlog to patch the patch...?

The mobile login page is the same as the desktop login page. This change relates to desktop CSS loading on mobile. The web team typically doesn't maintain this page (although cc @ovasileva as it sounds like we could benefit from some clarity around that).

It sounds like the guidance here, is to avoid any changes for mobile. If so, I've suggested an approach on the patch which keeps the status quo.

The web team typically doesn't maintain this page (although cc @ovasileva as it sounds like we could benefit from some clarity around that

Indeed, it looks like User login falls in the "Special pages" row on https://www.mediawiki.org/wiki/Developers/Maintainers, which says unmaintained 🙀

Theoretically I think the relevant component is MediaWiki-User-login-and-signup, maintained by the Platform team. Not sure how well they are set up to review frontend changes though.

I've added #platform-engineering as it looks like Special:UserLogin is in their domain.