Repository Wiki: Mermaid mindmap rendering issues in dark mode (“Dark default” theme)

[pwandzil]

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Hello,
I’ve noticed a diagram‑rendering issue in dark mode (“Dark default” theme (GitHub → Settings → Appearance)) when using the mermaid mindmap diagram type in a wiki page within my GitHub repository.

The issue is that GitHub’s native mermaid preview for mindmap diagrams does not correctly apply configuration files. As a result, the contrast is poor—for example, dark text on a dark background.

To demonstrate that this is specific to GitHub, I rendered the same diagram using the Mermaid Preview extension for VS Code (https://github.com/Mermaid-Chart/vscode-mermaid-preview). It wasn’t perfect, but at least the contrast was acceptable (light text on a dark background).

The issue seem only applicable to "mindmap type", different than:

• https://github.com/orgs/community/discussions/12116
• https://github.com/orgs/community/discussions/35733

I’ve prepared a demo wiki page here:
https://github.com/pwandzil/LifeHacks/wiki/From-Tony-Buzan-to-Github-Mermaid

Also short demo below:

Render issue

source code:

---
config:
  theme: 'dark'
---

mindmap
  root((mindmap))
    Origins
      Long history
        Facebook post by Tony Buzan in 1970s
      Popularisation
        British popular psychology author Tony Buzan
    Research
      On effectiveness<br/>and features
      On Automatic creation
        Uses
            Creative techniques
            Strategic planning
            Argument mapping
    Tools
      Pen and paper
      Mermaid

Github native render test (dark-default theme):

---
config:
  theme: 'dark'
---

mindmap
  root((mindmap))
    Origins
      Long history
        Facebook post by Tony Buzan in 1970s
      Popularisation
        British popular psychology author Tony Buzan
    Research
      On effectiveness<br/>and features
      On Automatic creation
        Uses
            Creative techniques
            Strategic planning
            Argument mapping
    Tools
      Pen and paper
      Mermaid

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Png:

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[queenofcorgis]

@pwandzil thanks for reporting this and helping improve our products! Confirming when I click your demo in dark default I have the same contrast issues. This was very thoroughly posted thank you for including so many helpful examples, our review team appreciates it.

[pwandzil]

I'm glad you could easily reproduce it!
As below, it seems that none of the mermaid "config" other than "theme" seem to work in either environments, "themeVariables" seem to be ignored and we see some kind of default coloring for a theme.

One information I missed to provide was versions:

• [Broken] Github's Mermaid info version was: v11.12.2
• [OK] vscode-mermaid-preview Mermaid info version was: v11.9.0-b.1

Also tried now another plugin and embed it in the markdown file in VSCODE:

• [Broken] shd101wyy.markdown-preview-enhanced
  Mermaid info version was: v11.12.1

markdown

```mermaid
info
```

```mermaid
---
config:
  theme: 'dark'
  themeVariables:
    nodeTextColor: '#cdd6f4'
    primaryTextColor: '#cdd6f4'
    lineColor: '#89b4fa'
---

mindmap
  root((mindmap))
    Origins
      Long history
        Facebook post by Tony Buzan in 1970s
      Popularisation
        British popular psychology author Tony Buzan
    Research
      On effectiveness<br/>and features
      On Automatic creation
        Uses
            Creative techniques
            Strategic planning
            Argument mapping
    Tools
      Pen and paper
      Mermaid
```