do_action( 'enqueue_block_editor_assets' )
Fires after block assets have been enqueued for the editing interface.
add_action on any hook before ‘admin_enqueue_scripts’.
In the function call you supply, simply use
wp_enqueue_style to add your functionality to the block editor.
View all references
do_action( 'enqueue_block_editor_assets' );
Bug / undocumented feature:
If you are wondering why your styles are not added to the Full Site Editor, they will only be added if they contain a class starting with “.wp-block-” such as .wp-block-xyz, if no such class is detected, then the FSE will not load your file.