Page border color setting is not exposed

[WhitespaceQ]

Librera has a virtual page that can be zoomed in/out when reading epub, this page has border with color that cannot be altered and it is a distraction in a pure black AMOLED theme.

I've tried looking through app-Librera.css but haven't find any relevant styling for the pages.

I recommend:

1. Expose the page border size and color through setting
2. Comment the css used in the apps with the description and where they're applied

Zoomed out, full screen view of the page border in question: