a bunch of res nightmode fixes

- removed res default background for active element in comment page
- lighten entries of .flat-list.buttons when hovered
- lighten colors of markdown links
- use parent's text color for headings and force them to not have
  background
- nicer (?) codeblock
- lighten spoiler
- darken live preview and wiki text background
- darken toc
- darken char counter
- darken author username background
- darken table
darken res big editor and live preview