change scrollbar css

[zeemood]

What's the purpose of this PR

Make scrollbar visible and beautiful. For the scene of hundreds config items, it seems like that a scrollbar takes me more convenience because of its high scrollview

Which issue(s) this PR fixes:

Fixes #

Brief changelog

change scrollbar css

Follow this checklist to help us incorporate your contribution quickly and easily:

• Read the Contributing Guide before making this pull request.
• Write a pull request description that is detailed enough to understand what the pull request does, how, and why.
• Write necessary unit tests to verify the code.
• Run mvn clean test to make sure this pull request doesn't break anything.
• Update the CHANGES log.

[github-actions]

CLA Assistant Lite bot All contributors have signed the CLA ✍️ ✅

[zeemood]

I have read the CLA Document and I hereby sign the CLA

[codecov-commenter]

Codecov Report

Merging #3925 (3016abf) into master (f909b8d) will increase coverage by 0.03%.
The diff coverage is n/a.

@@             Coverage Diff              @@
##             master    #3925      +/-   ##
============================================
+ Coverage     50.81%   50.84%   +0.03%     
  Complexity     2468     2468              
============================================
  Files           475      475              
  Lines         14608    14608              
  Branches       1523     1523              
============================================
+ Hits           7423     7428       +5     
+ Misses         6655     6651       -4     
+ Partials        530      529       -1     

Impacted Files	Coverage Δ
...mework/apollo/portal/component/PortalSettings.java	65.62% <0.00%> (+7.81%)	⬆️

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[nobodyiam]

This feature looks great! Would you please also update the CHANGES.md?