New enforced border style in WordPress 7.0

[markhowellsmead]

Description

There is a new CSS rule in 7.0 - html :where([style*=border-color]) - which enforces border-style: solid;. Where a border-style and border-color are defined on an element with no explicit border-width, browsers interpret this and enforce a default border width on elements which have no border-width explicitly defined. This means that after updating, some elements now have a visible border in the default state where they didn't in WordPress 6.9. This breaks layout and visual styling.

Step-by-step reproduction instructions

1. Add a border colour to an element but do not define a border style or border width.

Screenshots, screen recording, code snippet

No response

Environment info

No response

Please confirm that you have searched existing issues in the repo.

• Yes

Please confirm that you have tested with all plugins deactivated except Gutenberg.

• Yes

Please confirm which theme type you used for testing.

• Block
• Classic
• Hybrid (e.g. classic with theme.json)
• Not sure

[talldan]

Thanks for reporting. It should be fixed via #77476. Fix should be in 7.0.1 and Gutenberg 23.4.