Fix background (again) for ipywidgets (#11062)

[rchiodo]

Port of d96be50 to release

[sonarqubecloud]

Kudos, SonarCloud Quality Gate passed!

0 Bugs
0 Vulnerabilities (and 0 Security Hotspots to review)
0 Code Smells

No Coverage information
0.0% Duplication

[codecov-io]

Codecov Report

Merging #11064 into release-2020.04 will decrease coverage by 0.02%.
The diff coverage is n/a.

@@                 Coverage Diff                 @@
##           release-2020.04   #11064      +/-   ##
===================================================
- Coverage            61.27%   61.25%   -0.03%     
===================================================
  Files                  593      593              
  Lines                32492    32492              
  Branches              4593     4593              
===================================================
- Hits                 19910    19903       -7     
- Misses               11580    11585       +5     
- Partials              1002     1004       +2     

Impacted Files	Coverage Δ
src/datascience-ui/react-common/arePathsSame.ts	75.00% <0.00%> (-12.50%)	⬇️
src/client/common/utils/platform.ts	64.70% <0.00%> (-11.77%)	⬇️
src/client/linters/pydocstyle.ts	86.66% <0.00%> (-2.23%)	⬇️
src/client/datascience/debugLocationTracker.ts	76.56% <0.00%> (-1.57%)	⬇️
...client/datascience/kernel-launcher/kernelFinder.ts	75.70% <0.00%> (-0.94%)	⬇️
src/client/common/process/proc.ts	14.49% <0.00%> (-0.73%)	⬇️

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