6.6 Specificity/Style tracking issue

[talldan]

To do / Needs investigation

• Button outline style not working on hybrid themes after v6.6 #64225
• Block style variations now use hashed classnames, specificity issues #64856
• Feedback: It is confusing that adding background color also adds padding. #30725

In progress

• Retain the same specificity for non iframed selectors #64534 (this PR is quite large in scope, so a discussion might be needed around whether it's ok for 6.6)

Done (but needs core commit or cherry pick)

Awaiting auto cherry-pick

Released in 6.6.2

• Fix bumped specificity for layout styles in non-iframed editor #64076
• Global Styles: Fix block custom CSS pseudo element selectors #63980
• Fix block library and global styles stylesheet ordering when a block style variation is active #63918 (https://core.trac.wordpress.org/ticket/61748)
• Ensure root selector (body) is not wrapped in :root :where() #63726 (https://core.trac.wordpress.org/ticket/61704)
• Update postcss-prefixwrap dependency to 1.51.0 to fix prefixing in :where selectors #64458
• Featured Image Block: Reduce CSS specificity #64463

Released in 6.6.1

• Elements: Avoid specificity bump for top-level element-only selectors #63403
• Navigation block: Allow themes to override block library text-decoration rule #63406

[annezazu]

Thank you for opening and tracking this <3

[t-hamano]

I submitted #64785 regarding the conflict between element-level margin and layout-level margins.

[WilliamLeeks]

#65329

theme.json is not overriding core styles when targeting nested elements.