This theme is not actually shipped with NetNewsWire as a theme and has instead been reconstructed from the HTML and CSS in the app bundle. This is the theme that is preset in NetNewsWire.
A variation on the default theme with the font set to Atkinson Hyperlegible and the font size increased. Both of these changes lead to a much higher readability.
This theme does not differentiate between light and dark modes but is pleasent on the eyes.