Neatness is a MarkText export theme for document export to PDF / HTML.
It extends the default github-markdown.css used by the app.
Have a look at MarkText's documentation for full details: Themes (Export)
Basically you copy the .css file to themes/export/ inside the application data directory, e.g. for Windows this would be in %APPDATA%\marktext, and then restart MarkText.
When running Export, select the new theme from the Theme tab in the Export Options dialog.
