Typography: Fix link font-size inheritance when block typography is customized

[dpmehta]

What?

Closes #64976

This PR resolves an issue where custom typography font sizes applied to a block (via Inspector Controls) are ignored by the block's inner links if a global link font size has been defined in the Site Editor.

Why?

When a site-wide link font size is defined in Global Styles (Editor > Styles > Typography > Elements > Links), WordPress outputs an explicit styling rule: a:where(:not(.wp-element-button)) { font-size: ... } which carries a specificity of 0-0-1.

When a custom typography size is applied to a block, Gutenberg targets the block's wrapper (e.g., via a .has-large-font-size class or an inline style="..." attribute). Because the inner <a> element has a dedicated CSS rule targeting it via Global Styles, it fails to inherit the font size from its parent wrapper, creating visual inconsistencies where links don't match the surrounding block text.

How?

• Global Cascade Reset (packages/block-library/src/common.scss): Added a targeted :where() selector to capture wrappers containing custom typography features (.has-custom-font-size, [class*="-font-size"], and [style*="font-size"]). This rule forces inner anchor tags to font-size: inherit;. Wrapping it in html :where(...) provides exactly 0-0-2 specificity—strong enough to override the global 0-0-1 link rule, but weak enough to not disrupt any utility classes applied directly to the anchor elements themselves.

Testing Instructions

1. Using a block theme (e.g., Twenty Twenty-Five), go to Site Editor > Styles > Typography > Elements > Links, and set the Font Size to Large.
2. Edit a page or template, create a Paragraph block, and insert a hyperlink into the body text.
3. Select the Paragraph block and change its typography Font Size to Small via the Inspector Controls.
4. Verify that the link text shrinks to properly match the Small size of the paragraph instead of staying stubbornly Large.

Screenshots or screencast

Before Fix

before-fix.mov

After Fix

after-fix.mov

Use of AI Tools

AI was used to investigate the exact CSS specificity clash causing the inheritance breakdown and draft this PR description.

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Co-authored-by: dpmehta <mehtadev@git.wordpress.org>
Co-authored-by: NikoVee <nikov@git.wordpress.org>

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