I see I brought up the issue of Gutenberg mangling CCS code over a year a go in another post:

https://wordpress.org/support/topic/gutenberg-editor-destroying-ccs-code/

Any chance a Gutenberg block could be created for CCS code so it doesn’t get mangled? Adding it to a shortcode block doesn’t quite work, as it sees a problem every time. I mean it works, but it’s annoying to have to convert it every time to HTML.