Minor refinements on 0.22.x style updates

[petemill]

Description

#12565 introduced some tab style and preview-animation updates. As a result of making it to beta, there is some feedback (internal and external) to be addressed ahead of release. If the requested changes are kept small (e.g. color values or animation timings), then I will combine them to this one issue with 1 PR, and we can merge at an appropriate period to minimize extra merges / testing / builds, but still allow some builds to be created with these tweaks ahead of the release.

Requested changes:

• Adjust other 'grey' colors by approximately 5% (blue) to go with the new tabs bar colors
  • Preferences page section title gradient / selected title
  • bookmarks hover / text
  • shields panel background
  • alert background
• Reduce timing of content area preview fade-out (back to active tab) by 50%, but leave Tab element timing: Tab style updates x 8 #12565 (comment)
• Consider a tweak to favicons on theme colors - https://codepen.io/petemill/pen/XVovva
  • Currently using Option 2, considering Option 3 or 4