Since zed-industries/zed#48109, the C directive highlighting has been broken (see zed-industries/zed#49024). This is probably because this theme does not defines a preproc color field. We should add it to the recognized types.

At the same time, it would be nice to check if all zed's officially supported language elements are also supported in this theme (see https://zed.dev/docs/extensions/languages?highlight=highl#syntax-highlighting).