[Feature] Support dark mode

[Xiaokang2022]

When using theme mkdocs-material, the color of markmap doesn't automatically switch with the color mode, making it hard to see the content of markmap in dark mode.

I hope that when switching themes, color of markmap can adjust automatically.

• light mode:

• dark mode:

[Xiaokang2022]

Maybe it's not that markmap doesn't support dark mode, but that there are some bugs? I'm not sure.

Versions of my pakages:

• mkdocs: 1.6.1
• mkdocs-material: 9.6.15
• mkdocs-markmap: 2.5.2