[mermaid] text not legible in dark mode

Bug description

Diagrams that are legible in light more are not in dark mode, because the text colour doesn't appear to change.

Steps to reproduce

I created a data-intuitive/mermaid-demos-in-quarto repository reproduce and compare the mermaidjs demos.

An example that demonstrates this issue is this one: https://mermaid-demos-in-quarto.netlify.app/syntax/flowchart#graph-declarations-with-spaces-between-vertices-and-link-and-without-semicolon

In light mode using quarto 1.5.54:

In dark mode:

If it's ever necessary, I can update this demo page to verify whether the problem has been solved!

Expected behavior

This is the same diagram on the mermaid docs: https://mermaid.js.org/syntax/flowchart.html#graph-declarations-with-spaces-between-vertices-and-link-and-without-semicolon

In light mode:

In dark mode:

Actual behavior

No response

Your environment

• quarto 1.5.54, which uses mermaid 10.2.0 rc2
• mermaid diagrams fetched from mermaid 10.2.4

Quarto check output

$ quarto check
Quarto 1.5.54
[✓] Checking versions of quarto binary dependencies...
      Pandoc version 3.2.0: OK
      Dart Sass version 1.70.0: OK
      Deno version 1.41.0: OK
      Typst version 0.11.0: OK
[✓] Checking versions of quarto dependencies......OK
[✓] Checking Quarto installation......OK
      Version: 1.5.54
      Path: /home/rcannood/.local/share/quarto-1.5.54/bin

[✓] Checking tools....................OK
      TinyTeX: (not installed)
      Chromium: (not installed)

[✓] Checking LaTeX....................OK
      Using: Installation From Path
      Path: /usr/bin
      Version: 2023

[✓] Checking basic markdown render....OK

[✓] Checking Python 3 installation....OK
      Version: 3.12.4
      Path: /usr/bin/python3
      Jupyter: 5.7.2
      Kernels: python3

[✓] Checking Jupyter engine render....OK

[✓] Checking R installation...........OK
      Version: 4.3.3
      Path: /usr/lib64/R
      LibPaths:
        - /home/rcannood/R/x86_64-redhat-linux-gnu-library/4.3
        - /usr/lib64/R/library
        - /usr/share/R/library
      knitr: 1.47
      rmarkdown: 2.27

[✓] Checking Knitr engine render......OK

Start by rendering the linked mermaid-demos-in-quarto example with Quarto 1.5.54 and compare its generated diagram in light and dark modes. Inspect how Mermaid diagram text styling is handled, then verify that the text is legible in dark mode without regressing light mode.