needflow nodes extremely dark under dark mode (Sphinx 9.1.0, Sphinx‑Needs 7.0.0)

[piyenghar]

Environment:

OS: Windows 11

Sphinx: 9.1.0

Sphinx‑Needs: 7.0.0

Engine: tried both needs_flow_engine = "graphviz" and "plantuml"

Browser: one with forced dark mode (black boxes), one without (still quite dark)

Problem:

A simple .. uml:: PlantUML diagram renders with light boxes and dark text (looks fine).

The .. needflow:: assurance graph for my IEC 61508 SIL 2 Emergency Stop chain renders with very dark node backgrounds and very low text contrast. In a browser with forced dark mode the boxes look almost completely black.

Built‑in configs like :config: default (Graphviz) and :config: monochrome (PlantUML) do not significantly brighten the nodes.

Custom needs_graphviz_styles / needs_flow_configs attempts help only slightly; under dark mode the nodes remain much darker than normal UML diagrams.

Minimal needflow directive:

.. needflow::
:root_id: HAZ_ESTOP_01
:root_direction: both
:link_types: ADDRESSES,ALLOCATES,REFINES,REALIZES,VERIFIES,EVIDENCES,REVIEWS
:types: hazard,risk,sil,fsr,tsr,arch,verif,evidence,confirm
:show_link_names:
:root_depth: 10
:config: default # or monochrome

Request:

Is there a recommended “light”/high‑contrast style for needflow (PlantUML or Graphviz) that matches the docs examples?

If not, could you provide a sample needs_graphviz_styles / needs_flow_configs snippet that yields light node backgrounds and good contrast, suitable for browsers with forced dark mode?

I’ve attached:

The PNG of the needflow graph.