For #2271 - Fix hairline color on dark theme and private mode

[darkwing]

@AmyYLee

Pull Request checklist

• Tests: This PR includes thorough tests or an explanation of why it does not
• Screenshots: This PR includes screenshots or GIFs of the changes made or an explanation of why it does not
• Accessibility: The code in this PR follows accessibility best practices or does not include any user facing features. In addition, it includes a screenshot of a successful accessibility scan to ensure no new defects are added to the product.

After merge

• Milestone: Make sure issues finished by this pull request are added to the milestone of the version currently in development.

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[codecov-io]

Codecov Report

Merging #8839 into master will not change coverage.
The diff coverage is n/a.

@@            Coverage Diff            @@
##             master    #8839   +/-   ##
=========================================
  Coverage     19.02%   19.02%           
  Complexity      490      490           
=========================================
  Files           320      320           
  Lines         12843    12843           
  Branches       1688     1688           
=========================================
  Hits           2443     2443           
  Misses        10196    10196           
  Partials        204      204

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[boek]

Waiting on @AmyYLee to sign off

[darkwing]

@AmyYLee Screenshot with updated hairline:

[AmyYLee]

@darkwing Hi, I've posted the hex for the hairline colours without opacity. Also the background colours for the search bar without opacity.

[darkwing]

OK, updated screenshots with new colors:

[darkwing]

Another update with new background colors:

[AmyYLee]

@darkwing The above screenshots look good. Thanks!