[wp-trac] [WordPress Trac] #64408: Global Styles: Lift restrictions on global styles for classic themes

[WordPress Trac]

#64408: Global Styles: Lift restrictions on global styles for classic themes
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 Reporter:  youknowriad               |       Owner:  youknowriad
     Type:  enhancement               |      Status:  reopened
 Priority:  normal                    |   Milestone:  7.0
Component:  Themes                    |     Version:
 Severity:  normal                    |  Resolution:
 Keywords:  has-patch has-unit-tests  |     Focuses:
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Changes (by westonruter):

 * status:  closed => reopened
 * resolution:  fixed =>


Comment:

 In testing with Twenty Twenty-One, this change broke live preview in the
 Customizer. This was recently fixed in #63589.

 I'm also concerned about how this change moves the Customizer's Additional
 CSS into the global styles, as opposed to being printed separately as a
 `style#wp-custom-css` at the end of the `HEAD`. This introduces a change
 to the CSS cascade, which will likely cause unexpected styling issues. We
 were bit by this in 6.9 with
 [https://make.wordpress.org/core/2025/11/18/wordpress-6-9-frontend-
 performance-field-guide/#load-block-styles-on-demand-in-classic-themes
 loading block styles on demand in classic themes] (#64099, #64150). The
 change intended to make block styles load for classic themes in the same
 way they load for block themes, but the reality is that classic themes
 have been built in a way that a different CSS cascade is expected. This
 caused regressions: #64354. The workaround for sites in 6.9 is simply to
 opt-out of loading separate block styles, e.g. via the
 [https://wordpress.org/plugins/load-combined-core-block-assets/ Load
 Combined Core Block Assets] plugin. The [https://github.com/WordPress
 /wordpress-develop/pull/10601 pending PR] for 6.9.1 will hopefully
 eliminate the need for this by preserving the original CSS cascade in
 classic themes.

 However, no such workaround plugin would help sites that break due to a
 difference in the cascade for Additional CSS.

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Ticket URL: <https://core.trac.wordpress.org/ticket/64408#comment:4>
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