Thank you for the viewer improvements.
As mentioned, I think the default font color creates too much contrast and eye strain. macOS & iOS dark mode currently is also as such though macOS and iOS Books uses #BEBEBE as font color which is pretty nice in low or no light conditions. One possible option would be for the built-in themes to be customizable, e.g. one could set the font color and background for each theme and System would then use White or Black. One mention of high contrast causing eye strain:
https://blog.superhuman.com/how-to-d...s-7b3da644ff1f.
Another thing, is there any harm to also override the border-color of all elements? I'm not sure if in the case when there is no border, none would show up, and then if there is one, it would use the overridden night theme color for elements such as tables or divs.
Mentioned before, could there be a shortcut to bring up Preferences?