Great catch! Mermaid styling syntax (style and classDef directives) is on the roadmap for v0.3.0. Currently the diagrams render with Ferrite's theme colors (light/dark).

For privacy, you're in the right place — Ferrite's Mermaid rendering is 100% native Rust, no JavaScript, no external services, no network calls. All ~6000 lines of diagram rendering happen locally. We're even planning to extract this as a standalone crate so others can use it.