Wrong background makes equation preview invisible

Bug description

AFAICS recently VSCode stopped writing themes to settings.json and started saving them as part of the workspace state. This seems to confuse the quarto:equation preview panel, which now renders equations white on white when a light theme is active. One workaround is to explicitly set "workbench.colorTheme": "VS Code Light" in settings.json.

PS: while I was testing this I ran into https://github.com/quarto-dev/quarto/issues/703 again. Please give it a look, I provided an easy grammar fix.

Steps to reproduce

• Create qmd file
• Write $x^2$
• Position cursor inside the equation
• Open the quarto:equation preview

• Add "workbench.colorTheme": "VS Code Light" to settings.json
• Reload window
• Check again

Actual behavior

Renders equations white on white making them invisible.

Expected behavior

Should render equations white on dark or black on light according to the current theme.

Your environment

• IDE: VSCode 1.113.0
• macOS Tahoe

Start with the quarto:equation preview panel and reproduce the issue in VSCode 1.113.0 using a light theme, then compare theme detection when the theme is stored in workspace state versus settings.json. Done means equations render with suitable contrast: white on dark themes and black on light themes; reload the window and repeat the reproduction steps to verify both cases.