Support for richer styling in VS Code / positron

I'd like to request more customisation options for how quarto documents are presented in VS Code/Positron editor.

It makes sense to me that code blocks in the source view uses the editor theme. However, I'd like to have control over the font settings, background etc for all the non-code block parts of a quarto document.

The rationale is that users generally choose a theme based on what is most pleasant to code in, not what is most pleasant to read/write prose in. I personally prefer a dark theme for coding, but for writing longer texts I'd much prefer to do that on a light background with dark text. I also have monospaced typefaces I'd rather use for prose than for coding.

Begin by locating the VS Code/Positron editor integration and how it renders Quarto source documents. Define how users would configure font, background, and related styling for non-code content while leaving code blocks controlled by the editor theme. Done means the requested prose styling options are implemented and documented.