Eliminate white gap between black header and blue site title

[bobbingwide]

There's some white space between the header template part and the next block which is the site title.
This is partly due to the unwanted paragraphs in the inline CSS for the header.
There's already a fix but it's not in Gutenberg 10.4.1

I tried Gutenberg Nightly but that had its own problems.

Workaround

• Copy/cobble the override logic from fizzie and/or sb.
• Add some CSS overrides in style.css

[bobbingwide]

In addition to resolving the unwanted paragraphs added by wpautop()
it's also necessary to override some styling.

/**
Override top and bottom margins on h1 - user agent stylesheet
 */
h1 { margin-block-start: 0px; margin-block-end: 0px;}

also

/**
Override margin bottom added by Gutenberg inline styling
 */
.wp-block-columns { margin-bottom: 0px;}

[bobbingwide]

Reducing the bottom margin on columns resolved the problem that the header was too deep.

[bobbingwide]

Apparently you can use experimental-theme.json to set padding to 0.
I've asked how to do this in WordPress/gutenberg#30545 (comment)

[bobbingwide]

The template-part logic produces a Notice when a template part has been added to content but not actually selected.
The SSR tries to produce the message 'Template part has been deleted or is unavailable: %s'
But $attribute['slug'] is not set so the message is produced.
What should the code do? Be silent or produce a message?