make navbar sticky

[Jexsie]

Description of change

Checklist

• npm test passes
• documentation is changed or added (if applicable)
• permission has been obtained to add new logo (if applicable)
• contribution guidelines followed here

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[codecov]

Codecov Report

Attention: Patch coverage is 46.20690% with 156 lines in your changes missing coverage. Please review.

Project coverage is 80.10%. Comparing base (7982074) to head (3260218).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
src/pages/sustainers.tsx	0.00%	127 Missing ⚠️
src/components/NavBar/index.tsx	77.34%	29 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #770      +/-   ##
==========================================
+ Coverage   80.07%   80.10%   +0.03%     
==========================================
  Files         155      155              
  Lines       11664    11663       -1     
  Branches      865      865              
==========================================
+ Hits         9340     9343       +3     
+ Misses       2324     2320       -4     

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