Forms: use better default strategy for input styling

[CGastrell]

Fixes FORMS-299

Proposed changes:

This PR attempts to stabilize the fallback strategy for input background. The problem is one of balance between defaults, theme overrides and form elements trying to blend with the themes.
We're now trying to selectively declare the variable so it can be defaulted and we're using the default browsers use to style the inputs: field and fieldText to refer to CSS background-color and color properties.

Themes might always incur in overrides or lack of styling out of our control, we do our best to probe the styles and

Some themes were selected for showing symptoms of the issue, others because of popularity. Tested with:

• 2025
• 2024
• 2023
• 2021
• 2020
• Dravix
• Assembler
• Astra
• Hey
• Independent Publisher 2
• Livro
• Maywood
• Retrospect
• Rivington
• Shopall
• 2016
• 2010
• Varia
• Zoologist

Other information:

• Have you written new tests for your changes, if applicable?
• Have you checked the E2E test CI results, and verified that your changes do not break them?
• Have you tested your changes on WordPress.com, if applicable (if so, you'll see a generated comment below with a script to run)?

Jetpack product discussion

None

Does this pull request change what data or activity we track or use?

No

Testing instructions:

Add a form with as many fields as possible. Verify they look the same on editor and frontend.
Change both form and input backgrounds and verify again.
Some themes might lack styling or have purposely transparent backgrounds on inputs. This leads to unexpected results and will be defaulted to field color which, depending on dark/light theme, might become white/black.
See that input text is readable (good contrast), unless theme or custom colors make it otherwise.

[github-actions]

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  • Scheduled release: December 2, 2025

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[github-actions]

Are you an Automattician? Please test your changes on all WordPress.com environments to help mitigate accidental explosions.

• To test on WoA, go to the Plugins menu on a WoA dev site. Click on the "Upload" button and follow the upgrade flow to be able to upload, install, and activate the Jetpack Beta plugin. Once the plugin is active, go to Jetpack > Jetpack Beta, select your plugin (Jetpack), and enable the fix/forms-input-backgrounds-stabilizaation branch.
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bin/jetpack-downloader test jetpack fix/forms-input-backgrounds-stabilizaation

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[jp-launch-control]

Code Coverage Summary

This PR did not change code coverage!

That could be good or bad, depending on the situation. Everything covered before, and still is? Great! Nothing was covered before? Not so great. 🤷

Full summary · PHP report · JS report

_{Coverage check overridden by Coverage tests to be added later Use to ignore the Code coverage requirement check when tests will be added in a follow-up PR .}