Add styling to map popups

[arrested-developer]

relates #30

[codecov-io]

Codecov Report

Merging #32 into master will increase coverage by 0.73%.
The diff coverage is 100%.

@@            Coverage Diff             @@
##           master      #32      +/-   ##
==========================================
+ Coverage   98.56%   99.29%   +0.73%     
==========================================
  Files          11       11              
  Lines         139      142       +3     
  Branches       11       11              
==========================================
+ Hits          137      141       +4     
+ Misses          2        1       -1

Impacted Files	Coverage Δ
src/components/App.js	100% <ø> (ø)	⬆️
src/components/Map.js	93.75% <100%> (+9.13%)	⬆️

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 236d691...5484bd0. Read the comment docs.