* guix-hpc.scm (%default-special-prefixes)
(lex-scheme/guix): New variables.
(syntax-highlight): New procedure.
(read-markdown-page): Call 'syntax-highlight'.
* haunt.scm (post->sxml): Likewise.
* static/css/code.css: New file.
* static/css/main.css: Import it.
* guix.scm (guile-syntax-highlight): New variable.
Use it.