Post Editor: Requires default white background

[t-hamano]

Description

If a theme does not define a background color, you will see a black background in the Post Editor, making the text almost invisible. This issue does not occur on WP6.4.2 with the latest Gutenberg disabled.

The Site Editor applies a white background as a fallback. Like the Site Editor, the Post Editor also requires a white background as a fallback.

Similar PRs have been submitted in the past.

• Patterns: Apply white background to the preview as a fallback #54534
• [Site Editor]: Add default white background for themes with no background color set #46314

Step-by-step reproduction instructions

• Enable Emptytheme. This theme does not define a background color in theme.json.
• The Post Editor should have a black background color.
• The Site Editor should have a white background color.

Screenshots, screen recording, code snippet

544aed0983d52e4fae5eee2b10fcde56.mp4

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

[ramonjd]

I think maybe the background color for the .edit-post-visual-editor was introduced here: #50361

@talldan what do you think about perhaps making the default background color of the iframe.editor-canvas $white?

I think it still achieves what the original PR set out to do?

[talldan]

I think maybe the background color for the .edit-post-visual-editor was introduced here: #50361

Not something that I introduced, I modified to a slightly different shade in that PR.

I don't really know much of the background (ahem) of the background colors, so not sure I can lend good advice here. I think I did notice there were a couple of elements that had background colors, but I decided to tread lightly in that PR!

[ramonjd]

Ah, apologies. Thanks for the context though!