[Feature Request] mermaid threme follow preview theme automatically

[socay1]

Is your feature request related to a problem? Please describe.
if set preview theme to github-dark, the mermaid graphic will be unclear.
Sometimes, I only want to use github-dark in vscode, and Open in Browser is kept to github-light.

Describe the solution you'd like
If the mermaid theme could follow preview thrme, it will be great!
that is, when perview theme is dark, mermaid theme using dard css; and when preview is github-light, mermaid theme using default css.

Describe alternatives you've considered

Additional context