Egad, I've just almost completed reformulating my theme to take advantage of block-related css calls and structures (which are consistent only in their inconsistency). Dequeued the block editor css and replaced it with just the calls I needed. And I'll have to do it all again at the end of the year if the underlying template structure changes... so time to read up on full-site editing, I guess. Hurrah for the block library though, that's a useful addition