Handle adoptedStyleSheets

[edoardocavazza]

Introduce support for adoptedStyleSheets, as well as an improved shadow css implementation.

[codecov]

Codecov Report

Merging #69 (c801175) into master (ab1aa46) will decrease coverage by 4.55%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master      #69      +/-   ##
==========================================
- Coverage   93.65%   89.10%   -4.56%     
==========================================
  Files          20       20              
  Lines         694      707      +13     
  Branches      265      268       +3     
==========================================
- Hits          650      630      -20     
- Misses         16       40      +24     
- Partials       28       37       +9     

Impacted Files	Coverage Δ
src/Component.ts	90.78% <ø> (-1.32%)	⬇️
src/Interfaces.ts	100.00% <ø> (ø)
src/CustomElementRegistry.ts	69.81% <100.00%> (-24.53%)	⬇️
src/css.ts	100.00% <100.00%> (ø)
src/render.ts	92.02% <100.00%> (+0.04%)	⬆️
src/helpers.ts	80.39% <0.00%> (-17.65%)	⬇️
src/DOM.ts	80.64% <0.00%> (-16.13%)	⬇️

---

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 ab1aa46...c801175. Read the comment docs.