fix: correctly add or omit quotes around url() value

[bartveneman]

closes #144

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 100.00%. Comparing base (7b7fb26) to head (ddd359a).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff            @@
##              main      #145   +/-   ##
=========================================
  Coverage   100.00%   100.00%           
=========================================
  Files            1         1           
  Lines          332       336    +4     
  Branches       114       116    +2     
=========================================
+ Hits           332       336    +4     

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[codecov]

Bundle Report

Changes will increase total bundle size by 187 bytes (0.95%) ⬆️. This is within the configured threshold ✅

Detailed changes

Bundle name	Size	Change
formatCss-esm	8.49kB	187 bytes (2.25%) ⬆️

Affected Assets, Files, and Routes:

view changes for bundle: formatCss-esm

Assets Changed:

Asset Name	Size Change	Total Size	Change (%)
format-*.js	187 bytes	8.49kB	2.25%

Files in format-*.js:

• ./index.ts → Total Size: 14.37kB