mermaid diagrams are hard to see in dark mode

The brightness on my monitor is too high, so I view all sites in dark mode. In dark mode, on https://oss-docs.pages.dev/docs/architecture/ for example, the mermaid diagrams are pretty hard to see:

Dark mode screenshot:

Contrast that with light mode screen shot:

Start by opening the architecture documentation page at https://oss-docs.pages.dev/docs/architecture/ in both light and dark modes and compare the Mermaid diagrams with the screenshots in the issue. Trace where that page’s diagram styling is configured, then verify that the diagrams remain readable in dark mode without reducing light-mode clarity.

Written by the indexing model from the issue text.