Highlight.js Theme for EBNF

Problem

Extended Backus-Naur Form (EBNF) is supported by highlight.js, but the default theme has the appearance of no syntax highlighting. This likely applies to BNF and ABNF also.

Here are some examples:

GitHub

letter = "A" | "B" | "C" | "D" | "E" | "F" | "G" | "H" | "I" | "J" | "K" | "L" | "M" |
         "N" | "O" | "P" | "Q" | "R" | "S" | "T" | "U" | "V" | "W" | "X" | "Y" | "Z" |
         "a" | "b" | "c" | "d" | "e" | "f" | "g" | "h" | "i" | "j" | "k" | "l" | "m" |
         "n" | "o" | "p" | "q" | "r" | "s" | "t" | "u" | "v" | "w" | "x" | "y" | "z" ;
digit = "0" | "1" | "2" | "3" | "4" | "5" | "6" | "7" | "8" | "9" ;
identifier = letter , { letter | digit | "-" | "_"  } ;
topic = identifier , "/" , identifier ;
values = identifier , { ":" , identifier } ;
key = topic , "/" values ;

VS Code

MdBook

This is using the Ayu theme, but reverting to the default theme appears to produce similar results.

Proposed Solution

There's probably a way to custom the default them to make it work, but I'm 100% sure how. Ideally, the default theme should retain minimal syntax highlighting.

Notes

No response

The issue provides EBNF examples rendered in GitHub, VS Code, and MdBook, and focuses on the default theme's syntax highlighting. Start by reproducing the examples with the default theme and determine where the theme handles EBNF, BNF, or ABNF. Done means these code blocks retain minimal visible syntax highlighting without relying on a custom theme.