codex-styles seems to be loaded via JavaScript via @wikimedia/codex. That would mean this is subject to a flash of unstyled content in the display. @abi_ I think this might relate to the changes made in UniversalLanguageSelector to make the build compatible with MLEB.

Change 981572 had a related patch set uploaded (by Jdlrobson; author: Jdlrobson):

[mediawiki/extensions/UniversalLanguageSelector@master] Delay loading of Codex styles until they are needed

https://gerrit.wikimedia.org/r/981572

I haven't fully tested https://gerrit.wikimedia.org/r/981572 yet and am not 100% sure if this is the root of the problem. It doesn't explain the 3kb of extra CSS that is being loaded. @Catrope is it possible Codex-search bundle increased in size with the last release?

@Jdlrobson how urgent is this? We have a number of engineers out and may not be able to investigate until Monday.

Change 981198 had a related patch set uploaded (by Jdlrobson; author: Jdlrobson):

[mediawiki/extensions/UniversalLanguageSelector@master] Revert "Use Codex styles for buttons in language overlay"

https://gerrit.wikimedia.org/r/981198

Change 981198 merged by jenkins-bot:

[mediawiki/extensions/UniversalLanguageSelector@master] Revert "Use Codex styles for buttons in language overlay"

https://gerrit.wikimedia.org/r/981198

In T353071#9393405, @Jdlrobson wrote:

@Catrope is it possible Codex-search bundle increased in size with the last release?

The codex-search-styles module did increase slightly in size with the last release (1.0.1 -> 1.1.1), but the increase was only 140 bytes (29,053 -> 29,193).

@Jdlrobson yes I think the 3kB increase on beta can be attributed to Zebra. This is temporary. The way the Zebra module was constructed is that it is loaded on top of the default skins.vector.styles module.
I'm pretty confident that this performance loss will be regained when Zebra is merged into the default styles.

With the Vector master branch checked out, running a quick test on my local

$> curl "http://localhost:8080/w/load.php?lang=en&only=styles&skin=vector-2022&modules=skins.vector.styles" -so /dev/null -w '%{size_download}' | awk '{print $1/1024}'
> 66.125
$> curl "http://localhost:8080/w/load.php?lang=en&only=styles&skin=vector-2022&modules=skins.vector.styles" -so /dev/null -H 'Accept-Encoding: gzip,deflate' -w '%{size_download}' | awk '{print $1/1024}'
> 10.5869

shows that the current size of the skins.vector.styles module is 66.125 kB or 10.5 kB gzipped.

Running the same test with the WIP merge patch checked out, those curl commands show that the skins.vector.styles module is 52.94 kB or 9.97461 kB gzipped.
(Real world results will vary).

Change 981572 abandoned by Jdlrobson:

[mediawiki/extensions/UniversalLanguageSelector@master] Delay loading of Codex styles until they are needed

Reason:

Working on https://gerrit.wikimedia.org/r/c/mediawiki/extensions/UniversalLanguageSelector/+/981199 now the patch has been reverted.

https://gerrit.wikimedia.org/r/981572

I'm keeping an eye on the Grafana boards this week. So far I'm not seeing anything worrisome.