Background-agnostic version of the logo

[qexat]

For example, thick black border on the white version, and vice-versa.

It would be nice to avoid any logic - e.g. given that it is currently impossible to select a logo in a Markdown file without inline HTML which I try to avoid

[qexat]

An alternative idea would be to support the #gh-[light|dark]-mode-only thing but this would make it only work for GitHub