* Made notice Sass color mixing in based on $background-color and $text-color instead of hard-coded black and white values.
* Made some style adjustments to notices to improve readability.
Notice links are slightly darkened from the notice color, mostly because the gray-on-gray default notice links were very hard to read. Rather than being $notice-color, they are `mix(#000, $notice-color, 10%)`.
The notice background mix and code-background mix can now be set with the SCSS variables $notice-background-mix and $code-notice-background-mix.
The default mix for background was adjusted to 80%, from 90%.
The default mix for code-background was adjusted to 90%, from 95%.
Skins that still didn't read well were adjusted individually.
* Adjusted sunrise $notice-background-mix to 75%
* Adjusted dark theme notice background mix colors back to the default
Co-authored-by: Tom Manner <tsmanner@us.ibm.com>
