Mermaid sequence diagram numbers unreadable in dark mode

[alexhayes]

Contribution guidelines

• I've read the contribution guidelines and wholeheartedly agree

I've found a bug and checked that ...

• ... the problem doesn't occur with the mkdocs or readthedocs themes The diagrams don't work either with these things so not sure it's relevant.
• ... the problem persists when all overrides are removed, i.e. custom_dir, extra_javascript and extra_css
• ... the documentation does not mention anything about my problem
• ... there are no open or closed issues that are related to my problem

Description

Mermaid's Sequence Diagram can support auto-numbering of sequence numbers.

This works as expected (thank-you!), however when we switch to a dark theme, while the diagram switches, the numbers within the sequences become unreadable.

Expected behaviour

The sequence numbers are readable when in dark mode.

Actual behaviour

The sequence numbers are not readable when in dark mode as they are white on white.

Steps to reproduce

1. Apply the following diff against this repo

   diff --git a/docs/reference/diagrams.md b/docs/reference/diagrams.md
   index d6ce3a995..0521ef7cf 100644
   --- a/docs/reference/diagrams.md
   +++ b/docs/reference/diagrams.md
   @@ -91,6 +91,7 @@ between those actors:
    ```` markdown title="Sequence diagram"
    ``` mermaid
    sequenceDiagram
   +  autonumber
      Alice->>John: Hello John, how are you?
      loop Healthcheck
          John->>John: Fight against hypochondria
   @@ -106,6 +107,7 @@ sequenceDiagram
    
    ``` mermaid
    sequenceDiagram
   +  autonumber
      Alice->>John: Hello John, how are you?
      loop Healthcheck
          John->>John: Fight against hypochondria

2. Go to http://localhost:8000/mkdocs-material/reference/diagrams/?h=mermaid#using-sequence-diagrams

3. Toggle between light and dark mode.

Package versions

• Python: Python 3.10.7
• MkDocs: mkdocs, version 1.4.2 / ae7ed95
• Material: Version: 8.5.11

Configuration

As per https://github.com/squidfunk/mkdocs-material/blob/master/mkdocs.yml

System information

• Operating system: OSX
• Browser: Chrome

[squidfunk]

Thanks for reporting! Fixed in ee2c7ee. The fix will be released with the next beta of v9, tracked in #4714.