Cover block: Fix gradient overlay (remove black background color)

[webmandesign]

Description

Fixes #38764 by setting a transparent background color on a gradient overlay element so transparent gradient stops don't reveal a default black background color of an overlay.

Types of changes

Bug fix (non-breaking change which fixes an issue)

Checklist:

• My code is tested.
• My code follows the WordPress code style.
• My code follows the accessibility standards.
• I've tested my changes with keyboard and screen readers.
• My code has proper inline documentation.
• I've included developer documentation if appropriate.
• I've updated all React Native files affected by any refactorings/renamings in this PR (please manually search all *.native.js files for terms that need renaming or removal).
• I've updated related schemas if appropriate.

[glendaviesnz]

Thanks @webmandesign. This fix worked for me. I was able to replicate the issue with a non-block theme by adding the following to functions.php:

	add_theme_support(
		'editor-gradient-presets',
		array(
			array(
				'name'     => __( 'Red to transparent', 'test' ),
				'gradient' => 'linear-gradient(135deg, rgba(255,0,0,.8) 0%, rgba(255,0,0,0) 100%)',
				'slug'     => 'red-to-transparent',
			),
		)
	);

and the following css:

.has-red-to-transparent-gradient-background {
		background-image: linear-gradient(135deg, rgba(255,0,0,.8) 0%, rgba(255,0,0,0) 100%);
	}

Without this patch applied the default black background showed through the transparent part of the gradient instead of the background image:

With patch applied the image show through as expected in the editor and the frontend:

I also tested the following combinations on a non-block and blocked based theme and they all still functioned as expected with this patch applied:

• Cover with image showed default block overlay if no overlay color selected
• Cover with no image and solid overlay color selected
• Cover with image and solid overlay color selected

Given the recent issues with some of the Cover block CSS I think it would be good to get a second set of 👀 and approval on this before we merge it.

[andrewserong]

Thanks for the fix @webmandesign! This is testing nicely for me, too, it looks like it essentially overwrites the background-color: $black rule directly above it for those cases where the has-background-gradient class is applied.

I suppose an alternative would be to add an additional chaining to the :not rules above, but I quite like this separate rule as it's a bit more readable.

It also didn't look like the child combinator was necessary to me if you want to remove it (it seems to work well either way with nested cover blocks), so I'd be happy with it either way.

LGTM!

[webmandesign]

Thanks guys. I have updated the code and removed the child combinator.

[webmandesign]

Can I ask also for an opinion on #38761 (with #38762 fix)? Thanks.