Enqueue block custom CSS only when block renders on the page.

[isabel_brison]

Currently, block-specific custom CSS defined in theme.json or the global styles UI gets enqueued whether the block is on the page or not.

Custom CSS logic needs to be updated to more closely follow that of other global styles, so that block custom CSS can be enqueued conditionally in the same way as block global styles currently are.

Some of the changes from ​https://github.com/WordPress/gutenberg/pull/62357 can be brought into core.

Trac ticket: https://core.trac.wordpress.org/ticket/61395

Syncs changes from ​https://github.com/WordPress/gutenberg/pull/62357.

Thanks for reviewing, folks!

Can anyone reproduce this issue, or is it just my environment?

I could reproduce that locally; it was due to a missing check that made sure dequeuing customizer CSS only happened for block themes. I've replaced the check now so things should work exactly as they do in trunk.

I've just put up a PR to fix this in Gutenberg too: ​https://github.com/WordPress/gutenberg/pull/63331

Thanks for the quick fix 🚀

I could replicate the issue and can confirm the latest tweak in ​https://github.com/WordPress/wordpress-develop/pull/6750/commits/56d544825335a7b4e24bbf8aff4279c6db8e15f7 fixes it.

Before	After
<video src="​https://github.com/WordPress/wordpress-develop/assets/60436221/8f07093b-630c-4972-bf59-f25986a05963" />	<video src="​https://github.com/WordPress/wordpress-develop/assets/60436221/88247430-0ebb-41f0-828e-e9412fbaa859" />

[isabel_brison]

In 58703:

Editor: enqueue block custom CSS only when block renders on the page.

Updates the global styles custom CSS handling logic to be consistent with other global styles and take advantage of conditional enqueuing of block styles.

Props isabel_brison, aaronrobertshaw, andrewserong.
Fixes #61395.

Thanks for re-testing! Committed in r58703,

Thanks for committing this early in the 6.7 cycle ❤️