Better background contrast in dark mode

What does this MR do?

Start for #238824 (closed)

Bunch of small fixes for MR page in dark mode, plus a few global fixes. Main difference is more contrast between background and contentful elements.

Fixes the following:

1. More contrast for MR Widget items
2. Pipeline status icon backgrounds are now #333 instead of gross white
3. Make input background the same as input-wrapper (fixes filtered search)
4. Pipeline dropdown highlight color corrected
5. Make some random gray boxes same color as body background

Screenshots

before	after

NB the last screenshot was using #222 as background color

How to test?

To browse .com with these changes, you can copy this monster into a user stylesheet switcher (stylebot/stylus): https://gitlab.com/-/snippets/2039351