Bgashler1/color b

[bgashler1]

Alternate version, based on feedback from PR #8238.

Changes:

• Removed scroll decoration modifications (they are default now)
• Removed gradient trick and now instead use the viewlet background color so the tab well still is different from the find/replace. The first tab with its own background, in turn, is able to differentiate the tab well from the viewlet, so everything is clearly separated.
• Made inactive tabs have their own background color that is different from tab well.

This also addresses all feedback in #8564

Thanks @bpasero and @isidorn for your feedback. I'm sure we can continue refining this in July.

[mention-bot]

By analyzing the blame information on this pull request, we identified @bpasero and @isidorn to be potential reviewers

[bpasero]

Great, see my comment in #8564 (comment) why I did not just merge this PR directly but refined it a bit.