Improved contrast of usernames, hashtags and @s against reply box,
account bio field box contents, icons/buttons, left panel UI elements,
toot borders, etc
Added CR value notes to all colors
Made indentation consistent
Also from 4.14 (fail) to 5.52 (AA) on highlighted toot (though I can't
find in the generated CSS currently where the highlighted toot background
color is coming from; this may not be as bad when the $ui-base-color is
properly updated, if the highlight color is derived from it)