A11Y FIX: Specificity and other fixes for WCAG colors (PR #13082)

Looks like we lost some of these styles due to a specificity issue; when the wcag stylesheet uses the same classes as core, core styles win (looks like core styles are further down in the cascade after compiling)… wrapping everything with the html tag fixes it.

I also added some fixes to post controls because the existing styles were a bit of a mess.

Before:

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After:

Screen Shot 2021-05-18 at 12 54 39 AM

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GitHub