Custom markdown theme

**Is your feature request related to a problem? Please describe.**
No

**Describe the solution you'd like**
Maybe one can change the thme of the markdown with meta description?

**Describe alternatives you've considered**
I see goldmark-meta can get the metadata from markdown, and goldmark-highlighting can change the theme of the inline code, but i haven't found a solution to change the whole markdown theme

The issue mentions goldmark-meta and goldmark-highlighting as related Markdown tools, but names no files, tests, or entry points. Start by investigating how the plugin currently renders Markdown and whether metadata can define a complete theme; done would mean an agreed, implementable approach for changing the whole Markdown theme.

Written by the indexing model from the issue text.