Elements: Maintain backwards compatibility by avoiding specificity bump for top-level element-only selectors

[aaronrobertshaw]

When CSS specificity was capped at 0-1-0 for global styles via https://core.trac.wordpress.org/ticket/61165 it resulted in top-level element styles in some case having their specificity raised from 0-0-1.

This can be avoided and greater backwards compatibility maintained.

More info on the issue this causes can be found in:

• ​https://github.com/WordPress/gutenberg/issues/63345

This ticket tracks the syncing of PHP changes for the fix contained in:

• ​https://github.com/WordPress/gutenberg/pull/63403

[hellofromTonya]

Related #61660.

[hellofromTonya]

Elevating the priority to high for better tracking, as this issue is one of the drivers for a faster 6.6.1.

Testing has been happening on #61660 with good confirmation it resolves that issue.

Applied the diff of this PR to the 6.6 branch and followed the testing instructions. Looks ok 👍

[noisysocks]

In 58749:

Block Themes: Avoid specificity bump for top-level element-only selectors

Prevent issues (e.g. links being underlined) caused by a bump in CSS
specificity for top-level element-only global element styles.

Backports the PHP changes from ​https://github.com/WordPress/gutenberg/pull/63403.

Fixes #61630.
Fixes #61660.
Props aaronrobertshaw, andrewserong, noisysocks.

[ellatrix]

Reopening for backporting to the 6.6 branch.

[noisysocks]

Confusing that there's two tickets. Let's close this as a dupe of #61660 which has more comments.

Committed in r58749.

[hellofromTonya]

In 58751:

Block Themes: Avoid specificity bump for top-level element-only selectors.

Prevent issues (e.g. links being underlined) caused by a bump in CSS specificity for top-level element-only global element styles.

Ref: PHP changes from ​https://github.com/WordPress/gutenberg/pull/63403.

Reviewed by hellofromTonya.
Merges [58749] to the 6.6 branch.

Props aaronrobertshaw, andrewserong, noisysocks, annubis, butterflymedia, clarktbt, hellofromTonya, jorbin, joedolson, swissspidy, courane01, raquelandefeld, talldanwp, markhowellsmead, youknowriad, poena, cbirdsong.
Fixes #61630, #61660.

[hellofromTonya]

In 58757:

Editor: Update packages for 6.6.1.

Bugfixes included:

• ​Elements: Avoid specificity bump for top-level element-only selectors.
• ​Navigation block: Allow themes to override block library text-decoration rule.
• ​Fix invalid css for nested fullwidth layouts with zero padding applied.
• ​Prevent empty void at the bottom of editor when block directory results are present.
• ​Pattern overrides: Ensure "Reset" button always shows as last item and with border.
• ​Global Styles: Disable "Reset styles" button when there are no changes.
• ​Fix: Removed shuffle button when only 1 pattern is present.
• ​fix: wp icon focus issue.
• ​useBlockElement: return null until ref callback has time to clean up the old element.

Props ellatrix.
Fixes #61692.
See #61660, #61630, #61656.

[hellofromTonya]

In 58760:

Editor: Update packages for 6.6.1.

Bugfixes included:

• ​Elements: Avoid specificity bump for top-level element-only selectors.
• ​Navigation block: Allow themes to override block library text-decoration rule.
• ​Fix invalid css for nested fullwidth layouts with zero padding applied.
• ​Prevent empty void at the bottom of editor when block directory results are present.
• ​Pattern overrides: Ensure "Reset" button always shows as last item and with border.
• ​Global Styles: Disable "Reset styles" button when there are no changes.
• ​Fix: Removed shuffle button when only 1 pattern is present.
• ​fix: wp icon focus issue.
• ​useBlockElement: return null until ref callback has time to clean up the old element.

Reviewed by spacedmonkey.
Merges [58757] to the 6.6 branch.

Props ellatrix.
Fixes #61692.
See #61660, #61630, #61656.