[FEAT. REQUEST] Mirror cursor selection in preview

[tareqdayya]

Hi there,

This is a feature request to have any text selected in the editor to be mirrored in the preview section (i.e. in the preview, highlight any text selected in the editor).

Willing to work on it if interested.

[octokatherine]

This seems like a good idea to me.

I would still like the style of the markdown to match GH markdown and not be obscured by the highlighting, so maybe we can do something subtle like a vertical green line on the left of the selected section.

Let me know if you still want to work on this @tareqdayya.