CSS class on the highlighted <pre> wrapper. Syntect runs in class-based
mode (ClassStyle::Spaced): spans carry space-separated, lowercased TextMate
scope atoms (e.g. keyword, string, constant numeric) and the colors live
in the shipped code.css, theme-aware for both light and dark. There is no
embedded syntect theme and no inline style="color:…".
The comrak options used across the whole pipeline (GFM + P0 extensions).
Single source of truth so the AST pass (Cluster B) and the one-shot render agree.