Minor addon ux tweaks

[domyen]

Issue: These are tiny UX improvements that I found as I was fixing other bugs

What I did

• Improve viewport readability in the tooltip by changing the format to {width}x{height} from {width}px-{height}px
• Render a color swatch in the background addon
• Improve consistency of the color swatches

How to test

• Click on the background addon and see that there are swatches
• Click on the viewport addon and see the new dimension format
• Click on the color blindnesss addon and see that there is a subtle border around the swatch

[codecov]

Codecov Report

Merging #5712 into next will decrease coverage by 0.01%.
The diff coverage is 0%.

@@            Coverage Diff             @@
##             next    #5712      +/-   ##
==========================================
- Coverage   33.25%   33.24%   -0.02%     
==========================================
  Files         648      648              
  Lines        9362     9365       +3     
  Branches     1355     1330      -25     
==========================================
  Hits         3113     3113              
- Misses       5634     5637       +3     
  Partials      615      615

Impacted Files	Coverage Δ
addons/viewport/src/Tool.js	0% <ø> (ø)	⬆️
addons/backgrounds/src/components/ColorIcon.tsx	0% <0%> (ø)	⬆️
addons/a11y/src/components/ColorBlindness.js	0% <0%> (ø)	⬆️
.../backgrounds/src/containers/BackgroundSelector.tsx	0% <0%> (ø)	⬆️

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[shilman]

@ndelangen This also touches those files that don't exist on release/5.0 (ColorIcon.tsx and BackgroundSelector.tsx)