Thanks for submitting this patch @webmandesign 🙇

I've tested and I'm fairly convinced the deleted rule isn't required. I would probably want to get a confidence check from @WunderBart who introduced it to fix a regression.

Balancing new features with backwards compatibility support is not easy.

It's part of the reason why older CSS rules are still in play.

So, if a site updates to a later version of Gutenberg – one that does not support the ::before pseudo-element – the site still may have posts with Cover Blocks that have been saved previously, with the older markup.

The older markup therefore still requires the corresponding, older styles so that it looks decent in the frontend.

However, I can't find a case in the deprecations where .has-background-dim::before is required for the reasons you mentioned in #38761 Previously.has-background-dim featured on the container element, hence the need for &.has-background-dim::before.

<div class="wp-block-cover has-background-dim" ...

but it'd still be good to get the 👌 from @WunderBart

FYI, I've tested this with WP 5.8.3 and WP 5.9 (where the HTML has been updated). Tried many different Cover block displays but surely I might have missed something - don't know what I don't know ;) From my perspective the fix should be backwards compatible.

Some more info I've found: the code I've removed was introduced in #36312

I might have missed something - don't know what I don't know

I know what you mean. 😄 In my testing the changes seem innocuous, and should be fine to merge, but I'd feel more confident after confirmation.

Some more info:
I checked if there was any WordPress release with the #36312 code and have found none.

The code was introduced on Nov 8, 2021 and there were WordPress 5.8.2 and 5.8.3 releases since. None of them contains the code, so it was not used in the wild (unless Gutenberg plugin is used on the website, which I understand would be more for testing purposes and is not recommended for live websites?).

Also according to https://developer.wordpress.org/block-editor/contributors/versions-in-wordpress/ it seems WP5.8 contained Gutenberg 10.7(.?), while the code was introduced in Gutenberg 11.8.2.

But I can see WordPress 5.9.1 was already released so unfortunately I have to wait for some future WP version to fix this. Meanwhile I've applied the code fixing this into my themes.