Paragraph: scope Global Styles selector to .wp-block-paragraph

[Kgupta62]

What?

Changes the Paragraph block's root CSS selector from p to p.wp-block-paragraph.

Why?

Fixes #77466.

The paragraph block's root selector was a bare p tag, which matched every <p> element on the page — including those inside Post Excerpt, Quote, and other blocks that render <p> children.

Because directly-applied CSS properties always beat inherited ones regardless of specificity, paragraph Global Styles would override block-specific styling. For example, setting a font-size on the Paragraph block via Global Styles would bleed into Post Excerpt, even if the excerpt had its own font-size set.

How?

Updated selectors.root and __experimentalSelector in packages/block-library/src/paragraph/block.json from "p" to "p.wp-block-paragraph".

The wp-block-paragraph class is always present:

• Editor: added by useBlockProps via defaultClassName (apiVersion > 1)
• Frontend: added by the render_block_core/paragraph filter in index.php

Updated three PHP test expectations that use get_stylesheet() (reads from registered blocks) to reflect the new selector.

Testing Instructions

1. Activate a block theme (e.g. Twenty Twenty-Five)
2. Go to Appearance → Editor → Styles → Typography → Text
3. Set a custom font size (e.g. 24px)
4. Add a Post Excerpt block to a template
5. Set a different font size on the excerpt block via Global Styles
6. Before: Excerpt inherits paragraph font size, ignoring its own styling
7. After: Excerpt respects its own Global Styles, paragraph styles only affect actual Paragraph blocks

[github-actions]

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[t-hamano]

Thanks for the PR. However, this change has significant backward compatibility implications, and it's worth noting that similar initiatives have been closed in the past. Perhaps we should first review the discussion in 47282 to clarify the best approach and the problems that need to be addressed. See #47282 for more details.

[Kgupta62]

@t-hamano Thanks for flagging this — I've gone through #47282 and the discussion there.

I understand the backward compatibility concerns with changing the paragraph selector. My PR is narrower than #47282 (just the selectors.root change, not className support), but the compat implications are similar.

The motivation here is a real bug: with selectors.root: "p", Global Styles for paragraphs generate :root :where(p) which matches every <p> on the page — including inner <p> elements in Post Excerpt, Quote, and other blocks. Since directly-applied styles beat inherited styles regardless of specificity, these paragraph styles override the parent block's styles.

Given the discussion in #47282, would an alternative approach work better here? For example:

• Only scoping the selector for specific style properties that cause the bleed
• Adding the fix on the affected blocks' side instead (making their inner <p> selectors more specific)

Happy to adjust the approach based on what the team prefers.