* Parse color_mode cookie in browser
* Update useTheme.ts
* Update use-theme.js
* Update use-theme.js
* Add support for dark_high_contrast
Per https://primer.style/css/support/theming
I also checked all the color mode options, this is the only additional working with Primer 20 so far
* Remove gray bg
* Remove type
* Use defaults instead of types for fn args
* Thicker types