fix: better way to extract css for csp environments

[nightwing]

fixes #4897

Description of changes:

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[codecov]

Codecov Report

Merging #4899 (1b0612b) into master (6ad3123) will decrease coverage by 0.00%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4899      +/-   ##
==========================================
- Coverage   85.75%   85.74%   -0.01%     
==========================================
  Files         539      539              
  Lines       40627    40624       -3     
  Branches     6420     6419       -1     
==========================================
- Hits        34839    34835       -4     
- Misses       5788     5789       +1     

Flag	Coverage Δ
unittests	85.74% <100.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
src/autocomplete/popup.js	78.09% <100.00%> (ø)
src/ext/code_lens.js	91.54% <100.00%> (ø)
src/ext/error_marker.js	84.00% <100.00%> (ø)
src/incremental_search.js	76.08% <100.00%> (ø)
src/keyboard/emacs.js	50.16% <100.00%> (-0.49%)	⬇️
src/keyboard/vim.js	89.54% <100.00%> (ø)
src/snippets.js	86.97% <100.00%> (ø)
src/editor.js	82.46% <0.00%> (-0.15%)	⬇️
src/range.js	85.41% <0.00%> (+0.69%)	⬆️

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[anthonyryan1]

I can confirm this pull request is generating the CSS properly to satisfy all of my testing.