Improve visibility of comments on dark themes

Comments when using dark themes were originally improved by
Ie8b624b4201de696e6cfa282dca5f6000b1a901d, however due to a refactor,
this CSS no longer worked in 2.11+. Update the CSS accordingly, and
add a few more improvements for line numbers and range comments when
using dark themes.

Bug: Issue 3714
Change-Id: I8c4c69cbd8e988861a8022b6c906f98c54314b40
1 file changed